Position tracking system

ABSTRACT

An optical position tracking system that tracks the position of objects, using light intensity and/or frequency with the application of geometry and ratios of detector responses, is provided, having light distributing and light detecting components that employ the concepts of constructive occlusion and diffuse reflection. Diffusely reflective cavities, masks and baffles are used to improve certain radiating characteristics of the distributing components and certain response characteristics of the detecting components, to tailor the radiation and detection profiles thereof, including them substantially uniform for all angles within a hemispheric area which the distributing and detecting components face. The distributing and/or detecting components are partitioned with specially-configured baffles. A partitioned distributor has distinct emission sections where the sections can emit spectrally-different or distinguishable radiation. A partitioned detector has distinct detection sections where the sections can detect radiation from different directions. The system may be variously configured, to use different combinations of partitioned and nonpartitioned devices. In most configurations, a single head module provides one set of directional data about two coordinates (e.g., ρ and Θ) for one reflector. An additional head module remotely positioned from the first head module can provide a second set of directional data for the reflector (e.g., ρ 2  and Θ 2 ), for cross-referencing with the first set of directional data to obtain positional data in three dimensions of the object being tracked. The system can also track multiple objects, using spectrally-different (or at least spectrally distinguishable reflectors) in conjunction with correspondingly spectrally-compatible sensors.

BACKGROUND OF THE INVENTION

The present invention relates generally to optical emitters anddetectors, and optical position tracking devices, in particular, opticaldevices having distinct radiation and detection properties that may beused to track position of objects, using a relatively small number ofoptical elements.

Position tracking is a growing technology with ever increasingapplications. For example, in the entertainment arena, position trackingin three dimensions is used in virtual reality simulation. Positiontracking is also used in the industrial arena, with applications inprocess control and robotics. The field of biomedics also uses positiontracking devices for tracking portions of a human body to determine thebody's motion patterns. Similarly in animation dynamics, the tracking ofmultiple body parts is used for controlling animated figures. Many otherapplications exist, for which position tracking is useful if notadvantageous.

Conventional position tracking can be broken down into two broadtechnologies, i.e., active systems and passive systems. Active systemsutilize active electronic elements on the objects being tracked. Forexample, the Polhemus' 3SPACE ISOTRACK II® system uses active magneticelements to create a dynamic magnetic field that is representative ofthe body's position. By sensing changes in the magnetic field, thesystem delivers all six axes of the object's spatial location.

Active systems are generally high-performance, high-end products.However, they can have disadvantages, including limited range of motion,metal interference, complex operation and high cost. In particular, therange of the magnetic field is typically limited, and trailingconnection wires are often a nuisance. Where the area of motion containssubstantial metal, mapping of the entire field is usually part of thesystem's required initialization.

In contrast, passive systems track objects without physical linksbetween the object and the system. Target points such as retroreflectors may be used, or image processing of a video image may beperformed. While passive systems are often less complex and lessexpensive compared to active systems, they are often lacking inresolution. Thus, for object recognition, passive systems typicallyrequire extensive image processing, which can increase costs and theprobability of errors. The use of reflectors avoids some of theseproblems, but not without introducing other problems, such as the needfor critical alignment and extensive initialization.

Aside from the various system limitations discussed above, the sensingcomponents of an optical detector, such as photodiodes or charge-coupleddevice (CCD), have their own limitations. While these components can bemade directionally-sensitive (e.g., with the provision of a slit, or theuse of Gray-coded multi-element arrays), the response is often limited.For example, they typically provide directional information orresolution about one axis only, and the sensor's accuracy is typicallylimited by the number of optical elements provided.

It should therefore be appreciated that there exists a definite need fora relatively simple and inexpensive position tracking system, which cantrack the position of an object along at least three axes, if not allsix axes to include objection rotation, using minimal electrical and/oroptical elements. It is desired that the system has low alignment andinitialization requirements and low processing demands. In that regard,it is desired that the system be structurally and electronically simple,while remaining capable of providing at least directional indicative ofthe direction along which the object is positioned relative to thesystem. It is further desired that the system be able to providelocational data inclusive of range data, along with directional data,for tracking an object in three dimensional space. The present inventionaddresses all of these desires and more.

SUMMARY OF THE INVENTION

The present invention resides generally in an optical position trackingsystem that tracks the position of objects, using light intensity and/orfrequency with the application of geometry and ratios of detectorresponses.

The present invention provides for the illumination of an area that maybe defined by spherical or hemispherical coordinates with a tailoredspatial intensity profile, and/or the detection of light associated withan object in the area, with the recognition that certain characteristicsor properties of the light detected are indicative of the relativeposition or movement of the object in the area. Advantageously, theinvention applies the concepts of constructed occlusion and diffusereflection to accomplish its purpose with improved efficiency.

The positioning tracking system in one embodiment includes a retroreflector that is affixed to the object being tracked, and a head modulethat includes a light distributor and a light detector. Constructedocclusion as employed by the present invention includes the use of amask that improves certain radiating characteristics of the distributorand certain response characteristics of the detector. For example, amask in a predetermined position enables the distributor to provide amore uniform radiation profile, and the detector to provide a moreuniform response profile, at least for elevations approaching thehorizon. In general, changing the position and/or size of the maskchanges the radiating and response profiles. The profiles may be furthermanipulated or enhanced with the use of a baffle, particular for theprofile at angles at or near the horizon. The baffle can be conical oran intersecting structure. Where the electromagnetic radiation utilizedby the present invention includes visible light, components includingthe mask and the baffle are formed of a Lambertian, polymeric materialhaving a reflectance of approximately 99% for visible wavelengths.

In accordance with a feature of the present invention, the distributionprofile of a constructively occluded distributor can be specificallytailored or made substantially uniform for over most, if not all,azimuths and elevations of a hemispheric area over the distributor.Correspondingly, the response profile of a constructively occludeddetector can be specifically tailored or made substantially uniform formost, if not all, azimuths and elevations of a hemispheric area over thedetector. In essence, constructed occlusion can render both thedistributor and detector uniformly omnidirectional in the hemisphericarea which the occluded device faces.

In order that the system track the position of a reflector (or point),or at least provide directional information for that reflector, the headmodule of the system includes a partitioned occluded device which may beeither the distributor or the detector. In particular, the use of apartitioning baffle in a distributor renders a partitioned distributorhaving distinct emission sections where the sections can emitspectrally-different or distinguishable radiation. Correspondingly, theuse of a partitioning baffle in the detector renders a partitioneddetector having distinct detection sections where the sections candetect radiation from different directions.

The system may be variously configured, to use different combinations ofpartitioned and nonpartitioned devices, that is, a partitioneddistributor with a nonpartitioned detector, or a nonpartitioneddistributor with a partitioned detector. A partitioned distributorprovides a plurality of radiation sections and a partitioned detectorprovides a plurality of detection sections. In most configurations, asingle head module provides one set of directional data about twocoordinates (e.g., ρ and Θ) for one reflector, using one of thesecombinations, wherein one of the devices is partitioned into foursections or quadrants.

An additional head module remotely positioned from the first head modulecan provide a second set of directional data for the reflector (e.g., ρ₂and Θ₂). By cross-referencing the second set of directional data withthe first set of directional data, the system is able to obtainpositional data in three dimensions of the reflector, that is, threecoordinates, along three axes for the reflector.

The system can also track additional reflectors, usingspectrally-different (or at least spectrally distinguishable reflectors)in conjunction with correspondingly spectrally-compatible sensors todistinguish between data collected for each reflector. Where the systemuses a head module having a nonpartitioned distributor and a partitioneddetector to detect one reflector, the system can use additional headmodules, each housing an additional set of sensors corresponding to anadditional reflector. However, the system can also use a single headmodule that is configured to house all of the additional sets ofsensors. In particular, the single head module can be configured havingone partitioned detector where each section houses a sensor from a setcorresponding to a reflector being tracked. Accordingly, a single headmodule can track multiple reflectors.

As variations on the head module described above, the nonpartitioneddistributor and the partitioned detector may use separate cavities orshare a single cavity within the head module. Moreover, as furthervariations, the nonpartitioned distributor of the head module may emitcontinuous broad band radiation or pulses of broad band radiation. Wherethe radiation is emitted in pulses, the elapsed time for the pulseradiation to reflect off the reflector can be analyzed by the system asdata providing a range coordinate for the tracked reflector. Using boththe intensity variation of the radiation, and the elapse time of thepulses, the system can derive all three coordinates for a reflector,without using a separate head module.

Because the system illuminates the detection zone without discriminatingbetween the object being tracked and any other extraneous objects, suchas furniture or walls, background or self illumination can besignificant and adversely affect the system's performance. Where sensorsof different or distinguishable spectral characteristics are used in thesystem for detecting multiple reflectors, the system provides a separateset of sensors dedicated to sensing background illumination so that theeffects of self illumination can be compensated.

The system may also be configured to reduce the level of backgroundillumination. In particular, the system utilizes a head module having ascanning beam source that is situated between a split partitioneddetector. The beam is of a predetermined width and sweeps the detectionzone in search of reflectors. With the beam illuminating only a portionof zone at any give time, background illumination is substantiallyreduced and the system is therefore available to perform a coloranalysis using a relatively small number of filter sensor combinationsto distinguish between a very large numbers ofspectrally-distinguishable reflectors. Like the previous embodiments,this embodiment uses two head modules to detect all three coordinates ofone reflector.

In an alternative embodiment also using color analysis, the system usesa head module that includes a nonpartitioned detector with a partitioneddistributor. The partitioned distributor houses in each section a lampof a distinguishable color (frequency), such that each section isdistinctly associated with a distinguishable color. In accordance withthe application of color analysis, the detector houses a smallcombination of filtered sensors. The color mix reflected by a reflectoris analyzed by the system to indicate a set of directional data for thereflector relative to the head module.

The system may also be configured as an optically active system, usingactive light sources, such as LEDs, that are placed on the object beingtracked, and a partitioned detector. In this embodiment, light emittedfrom the LEDs are detected by the partitioned detector, and the color oroscillation frequencies of the LEDs are used to distinguish betweendifferent LEDs.

Other optical devices and position tracking systems are contemplated bythe present invention. For example, an optical device configured as aring having two structures which selectively occludes the opticalsurface of the other for different elevation angles is provided. Again,the principles of constructed occlusion is applied such that the devicehas a tailored or substantially uniform profile which can render thedevice hemispherical as a radiator or a detector. To also render thedevice directional, the structure may be configured such to providedistinct and separate segments.

Other features and advantages of the present invention should becomeapparent from the following description of the preferred embodiments,taken in conjunction with the accompanying drawings, which illustrate,by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a position tracking system, inaccordance with the present invention, for determining and displayingthe position of game equipment;

FIG. 2 is a schematic diagram of a Lambertian surface, demonstrating thecosine dependence property associated therewith;

FIGS. 3A and 3B are schematic diagrams of a mask used to constructivelyocclude a Lambertian surface;

FIG. 4 is a side cross-section view of an optical arrangement employingthe concepts of constructive occlusion and diffusive reflection, inaccordance with the present invention;

FIG. 5 is a graph illustrating the cosine dependence of the arrangementof FIG. 4;

FIG. 6 is a side cross-section view of an optical arrangement employingthe concepts of constructive occlusion and diffusive reflection, and aconical baffle, in accordance with the present invention;

FIG. 7 is a graph illustrating the substantial alleviation or treatmentof the cosine dependence of the arrangement of FIG. 6;

FIGS. 8A and 8B are perspective views of an intersecting baffle, inaccordance with the present invention;

FIG. 9 is a perspective view of another intersecting baffle, inaccordance with the present invention;

FIG. 10 is a side cross-section view of an optical arrangement employingthe concepts of constructive occlusion and diffuse reflection, and theintersecting baffle, with treatment of the Fresnel reflection, inaccordance with the present invention;

FIG. 11 is a side cross-section view of an optical arrangement with aspecially configured mask having properties of a baffle;

FIG. 12A is a side cross-section view representative of a partitioneddistributor and a partitioned detector, in accordance with the presentinvention;

FIG. 12B is a cross section view of FIG. 12A, taken along line 12B--12B.

FIG. 13 is a perspective view of a head module used in association withan oscilloscope, in accordance with the present invention;

FIG. 14 is a conceptual representation of X-Y coordinates of a displayof the oscilloscope of FIG. 13;

FIG. 15 is a schematic diagram of the electronics for convertingelectrical signal from the head module of FIG. 13, to the X-Ycoordinates of the oscilloscope of FIG. 13;

FIG. 16 is a side cross-section view of an embodiment of the headmodule, in accordance with the present invention;

FIG. 17 is a cross-section view of FIG. 16, taken along line 17--17;

FIG. 18A is a side cross-section view of another embodiment of the headmodule, in accordance with the present invention;

FIG. 18B is a cross-section view of FIG. 18A taken along line 18B--18B;

FIG. 19A is a side cross-section view of a further embodiment of thehead module, in accordance with the present invention;

FIG. 19B is a cross-section view of FIG. 19A, taken along line 19B--19B;

FIG. 20A is a side cross-section view of yet another embodiment of thehead module, in accordance with the present invention;

FIG. 20B is a cross-section view of FIG. 20A, taken along line 20B--20B;

FIG. 21 is a perspective view of another embodiment of the system, inaccordance with the present invention;

FIG. 22A is a plan view of a platform on which four individualpartitioned detectors are mounted;

FIG. 22B is a side view of the platform of FIG. 22A;

FIG. 23A is a top plan view of another embodiment of an occluded devicein accordance with the present invention;

FIG. 23B is a side view of the occluded device of FIG. 23A;

FIG. 23C is a side view rotate 90 degrees from the view of FIG. 23B;

FIG. 24A is a perspective view of a ring detector in accordance with thepresent invention;

FIG. 24B is a top plan view of the ring detector of FIG. 24A;

FIG. 24C is a cross section view of the ring detector of FIG. 24A,demonstrating the substantially constant cross section area providedthereby;

FIG. 25A is a perspective view of a sectioned ring detector inaccordance with the present invention;

FIG. 25B is a top plan view of the ring detector of FIG. 25A;

FIG. 25C is a side view of the ring detector of FIG. 25A, demonstratingthe substantially constant cross section area provided thereby;

FIG. 26A is a top plan view of a multiple cavitied optical device inaccordance with the present invention;

FIG. 26B is a side cross-section view of the device of FIG. 26A, takenalong line 26B--26B;

FIG. 27A is a side cross-section view of another embodiment of anoptical arrangement employing the concepts of constructive occlusion anddiffusive reflection, and a baffle, in accordance with the presentinvention;

FIG. 27B is a view of the optical arrangement of FIG. 27A taken alongline 27B--27B;

FIG. 28 is a side cross-section view of two partitioned opticalarrangements configured back-to-back to provide spherical coverage inaccordance with a feature of the present invention;

FIG. 29A is a perspective view of two sectioned ring detectorsconfigured back-to-back to provide spherical coverage in accordance withthe present invention;

FIG. 29B is a side cross section view of the ring detectors of FIG. 29A;

FIG. 30A is a side cross section view of one embodiment of an azimuthaldevice in accordance with the present invention;

FIG. 30B is a view of the azimuthal device of FIG. 30A taken along line20B--20B;

FIG. 30C is a view of the azimuthal device of FIG. 30A taken along line30B--30B, with a tailored coverage;

FIG. 31A is a side cross section view of another embodiment of theazimuthal device in accordance with the present invention;

FIG. 31B is a view of the azimuthal device of FIG. 31A taken along line31B--31B; and

FIG. 31C is a view of the azimuthal device of FIG. 31A taken along line31B--31B, with a tailored coverage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the exemplary drawings, the present invention resides in anoptical position tracking system that tracks the position of an object,without requiring complicated electrical wiring, expensive photodetectorarrays, video cameras, or image processing. More specifically, thesystem measures optical properties such as light intensity and frequencyto provide at least directional data along two axes, if not positionaldata along three axes, for the object being tracked. If desired, thesystem may also provide positional and rotational data along six axesfor the object being tracked.

Referring to FIG. 1, the position tracking system has numerousapplications. For example, the system may be used in a video game 11,where signals representative of the position or movement of gameequipment within a zone Z are detected and processed, and converted tovideo signals fed to a video monitor. Though the system and display 15are shown outside the zone Z, these components may of course be insidethe zone Z.

One embodiment of the position tracking system 10 is shown in FIG. 1,having a head module H tracking a retro reflector RR1. In accordancewith a feature of the invention, the head module H utilizes the conceptsof constructed occlusion and diffuse reflection, both of which arediscussed below in further detail.

As background, constructed occlusion may be used to change certaincharacteristics of a substantially Lambertian surface, whether it is anemitter or a detector surface. A substantially Lambertian emitter X isshown in FIG. 2. While the emitter X is illustrated with a planarsurface, an emitter surface with substantially Lambertian propertiesneed not be planar.

It is observed that the radiation intensity of the emitter X varies withthe angle φ. Thus, the emitter X has a radiation intensity profile thatis a function of the angle φ. This function or relationship between theradiation intensity and the angle φ can be seen in the change in thecross sectional area K of the surface A as the angle φ changes. Inparticular, where φ is defined from the normal of the emitter surface A,the cross sectional area K varies as a cosine function of the angle φ.

FIG. 2 is also representative of a substantially Lambertian detector(also designated by X). While the detector X is shown with a planarsurface, a detector surface with substantially Lambertian propertiesneed not be planar. As the emitter X, the detector X has a responseintensity profile that is a function of the angle φ. Again, thisfunction can be seen in the change in the cross section area K, whichdecreases as the angle φ increases from the normal to the horizon.

Constructed occlusion aims to reduce, if not eliminate, the cosinedependency on the angle φ in both the emitter X and the detector X. Asshown in FIGS. 3A and 3B, a mask M is employed to constructively occludethe surface A. Properly sized and positioned from the surface A, themask M is rendered to selectively "block" portions of the surface A,such that the cross section area K remains constant for most angles ofφ. Accordingly, the mask M offsets the change in cross section area Ksuch that the radiation or response profile of the surface issubstantially uniform for angles of φ, except those near the horizon.For the configuration shown in FIGS. 3A and 3B, the cross section area Kremains constant for angles of φ between 0 and approximately 80 degrees.This range of angles varies with different geometry between the mask,aperture and cavity. Overall, the radiation or response profile may bedistinctly manipulated as desired with different mask and surfacegeometry.

While the mask M may be completely opaque, constructive occlusion may beachieved without complete opacity in the mask M. So long as the mask Mprovides a relative reduction in the transmission of radiation betweenoccluded and nonoccluded areas, the cosine dependence is altered.

As mentioned, the system also applies the concept of diffuse reflection.As background, a diffusive reflector can increase the efficiency of anoptical system by allowing a surface emitter or detector to be replacedby a point emitter or detector. For both cases, reference is made toFIG. 4.

A substantially Lambertian emitting surface LS can be created using apoint illuminating element 12 (such as a fiber optic) that illuminates acavity 16 whose interior surface 20 is diffusely reflective. The cavity16 diffusely reflects radiation from the point element 12 such that auniformly illuminated surface is created at the aperture 22 of thecavity 16. Correspondingly, a substantially Lambertian detection surfaceLS can be created using a point detecting element 12 (such as aphotodiode) that detects light within a cavity 16 whose interior surface20 is diffusely reflective. The cavity 16 diffusely reflects radiationentering the cavity 16 through the aperture 22 such that the pointdetecting element 12 uniformly detects radiation reaching the aperture22. It is understood by one of ordinary skill in the art that the pointelement 12 may be a device localized at the cavity 16, or alight-conveying device, such as a fiber optic 14 or an opticalwaveguide, that efficiently transmits light into or away from the cavity16 to another area.

With selective placement and/or sizing of the mask M above the aperture22, the occluded arrangement of FIG. 4 can either (i) illuminate an areaover the aperture 22 with an intensity profile that is substantiallyuniform in almost all directions of the area, as an occludeddistributor, or (ii) uniformly detect radiation over almost alldirections of the area, as an occluded distributor, where the area isreadily defined in rho and theta directions in spherical orhemispherical coordinates. The radiation and detection profiles canremain substantially uniform for most angles in accordance with theselected mask/cavity/aperture geometry, except for those angles at ornear the horizon of the occluded arrangement (hereinafter referred to asthe horizon district).

The cavity 16 of FIG. 4 can be provided in a base 18 which also providesa shoulder 28 surrounding the aperture 22 of the cavity. The base 18 maybe formed of aluminum, plastic, or like materials, and covered with acoating of diffusely reflective substance, such as barium sulfate, sothat the base 18 as a whole can diffusely reflect incident light. Thebase 18 may also be formed of a diffusely reflective bulk material suchas Spectralon® sold by Labsphere Inc., of North Sutton, N.H. Spectralon®is easily machined, durable, and provides a highly efficient Lambertiansurface having a reflectivity of over 99%, in visible and near-infraredwavelengths. Other suitable materials, though typically less effectivethan the diffuse reflective materials mentioned above, includequasi-diffuse reflective materials, such as flat white paint.

The mask M, in particular its underside 24, is also constructed of adiffusely reflective material, such as Spectralon®, so that any lightincident on the underside of the mask M is not lost but reflected backinto the cavity 16. The light redirected back into the cavity 16 is, onaverage, reflected many times within the cavity 16 and adjacentdiffusely reflective components.

The cavity 16 is illustrated as a hemispherical cavity; however, thecavity may be any shape. Moreover, the size of the aperture 22 need notbe comparable to the maximum cross-sectional area of the cavity; thatis, the cavity may be more spherical than hemispherical. Furthermore,the aperture 22 need not be planar. However, the hemispherical cavitywith a planar aperture may be preferred as it is easier to construct andit affords geometric symmetries that allow the use of simplifyingcalculations and assumptions.

Where the cavity 16 is hemispherical (or spherical) and the aperture 22planar, as shown in FIG. 4., the aperture 22 of the cavity 16 defines adiameter D_(a) and the mask defines a diameter D_(M). As mentioned, theratio between the diameters D_(a) and D_(M) is a parameter that canchange the profile (radiation or response) over the entire 2π steradianhemisphere which the occluded arrangement faces. In general, uniformityin the profile is increased if the mask/cavity diameter ratio is closeto one; however, this ratio reduces the efficiency of the occludedarrangement by diminishing the acceptance/escape area between the maskand the aperture. It is currently believed that by decreasing theintensity for certain angles while increasing the intensity for otherangles, the mask substantially averages the profile over a wide range ofangles, for a more uniform efficiency for most angles. A mask/cavitydiameter ratio of about 0.8 to 0.9 is preferred. This ratio provides areasonably level profile, while maintaining a relatively high level ofefficiency.

The distance or height D between the mask M and the aperture 22 isanother parameter that can change the occluded arrangement's radiationor detection profile. Moreover, the thickness of the mask M can alsochange the profile.

The graph of FIG. 5 shows the cross-sectional area K of an occludedarrangement with an aperture diameter of approximately 2.0", a mask witha diameter of approximately 1.8", and a separation distance between themask and aperture of approximately 0.3". It can be seen that the profileof this occluded arrangement remains relatively constant until φ reachesapproximately 80 degrees. Thereafter the profile drops dramatically.

As different profiles may be obtained with differentmask/cavity/aperture geometry, it may be useful to construct the cavityand mask out of a core material that is pliant, e.g., rubber, so thatthe cavity and/or mask may be readily reconfigured to provide differentgeometries with different radiation or detection profiles.

In order to expand the uniform portion of the profile into greaterangles of φ, that is, into the horizon district, the system 10 mayeither increase the energy of the illumination radiated or detected, orprovide a deflector or baffle 30 as shown in FIG. 6. The baffle 30 isconfigured to provide a surface 32 below the mask M, that issubstantially perpendicular to the horizon district. The surface 32serves to reflect light to the horizon district to significantlyincrease the illumination intensity in that district. Like the mask Mand the base 18, the baffle 30 is constructed out of a diffuselyreflective material such as Spectralon®. The reflectivity of the bafflescan be graded so that the baffle can have an angle dependentreflectivity, if desired, for example, to compensate nonuniform effects.

Used appropriately, the baffle 30, in conjunction with the shoulder 28,can extend the profile uniformity into angles of φ well beyond 90degrees (see, e.g., FIG. 7). For an occluded emitter arrangement, theshoulder 28 redirects toward the upper hemispheric area that wouldotherwise be directed below the horizon. For an occluded detectorarrangement, the shoulder 28 blocks light from below the horizon.

As mentioned, the radiation or detection profile over the hemisphericarea may be tailored as desired by carefully configuring anddimensioning the cavity aperture 22, the mask M, the baffle 30, and/orthe shoulder 28. For example, referring to FIG. 7, an occludeddistributor R having an aperture with a diameter Da of approximately2.0", that is constructively occluded by a mask M with a diameter D_(M)of approximately 1.8" and enhanced by a baffle 30 having a base ofapproximately 0.27" in diameter and approximately 0.21" in length, has aradiation intensity profile that is relatively constant for angles of φup to 90 degrees.

Other baffles can be equally effective at increasing the intensity inthe horizon district. For example, FIG. 11 shows a baffle that isincorporated into the mask M by bevelling edges 48 of the mask M. Wherethe mask M has a substantial thickness, the bevelled edges 48effectively can direct light to the horizon district.

Referring to FIG. 8A, an alternative embodiment of the baffle is shown.Also covered with a diffusely-reflective material, a baffle 41 is formedof multiple extended members 42 defining an intersection 43 at theirmidpoints. The members 42 are preferably planar, but they may be curvedor otherwise. The baffle 41 preferably, but not necessarily, definessymmetrical sections S in the occluded arrangement.

The baffle 41 preferably, but not necessarily, has a length 44substantially equal to the diameter of the aperture 22. Alternatively,the length 44 may be longer to extend beyond than aperture 22, or beshorter and shy of reaching the aperture 22. The baffle 41 preferably,but not necessarily, has a height 46 substantially equal to theseparation distance D between the mask M and the aperture 22.Alternatively, the height 46 may be greater or lesser than theseparation distance D. Like the baffle 30, the baffle 41 extends towardthe aperture 22 of the cavity 16 to create a substantially perpendicularsurface 32 relative to the horizon. Consequently, the baffle 41increases the illumination intensity at the horizon district for a moreuniform profile (radiation or response) in the horizon district.

The baffle 41 may be modified as desired to change the profile. Amodified baffle 41' is shown in FIG. 8B. The baffle 41' compared to thebaffle 41 has an enlarged core 45 at the intersection 43. Although thecore 45 is illustrated with a circular cross section, the core 45 may bedifferent shapes. The baffle 41' may also have greater thickness 47 inthe members 42.

To obtain a relatively uniform profile, the arrangement of FIG. 10 usesa mask diameter D_(M) of approximately 1.8" and an aperture diameterD_(a) of approximately 2.0", which results in a mask/aperture diameterratio of approximately 0.9 or 90%. A mask/aperture diameter ratio of 0.9provides a relatively uniform response over a relatively large range ofthe angle φ while maintaining an acceptable range of operation. Further,the disk-shaped mask M is spaced away from the aperture 22 byapproximately 0.3 inches, resulting in a mask distance to aperturediameter ratio of approximately 0.2 or 20%.

The arrangement of FIG. 10 may be enclosed in a cover, e.g., dome 38, toprotect the interior components. Moreover, the arrangement of FIG. 10shows the point element 12 being mounted but rather below the mask M andbaffle 41, outside of the cavity 16. Connection wires 40 from the pointelement 12 may be inserted through bores provided in the mask andbaffle.

With the point element 12 facing the aperture 22 from the underside ofthe mask M, "hot spots" that may result from direct angles of radiationor detection into the cavity 16 can be substantially avoided. By"inverting" the point element 12, effects of Fresnel reflection, whichwould otherwise increase the cosine dependence of the arrangementprofile, may also be avoided. Fresnel reflection generally occurswhenever light travels through a surface between two materials havingdifferent indices of refraction, for example, air and glass or silicon.Much like the cosine dependence of the Lambertian surface on the angle φdiscussed above, Fresnel reflection increases with the angle φ, whichdecreases the illumination intensity of light in the horizon district.

The arrangement of FIG. 10 illustrates the concepts used by the system.The head module H of the system 10 in certain embodiments includes anoccluded and baffled emitter (distributor R) and in other embodiments,an occluded and baffled detector (detector T). Occluded and baffleddistributors and detectors are disclosed, respectively, in U.S.application Ser. No. 08/590,290, filed Jan. 23, 1996 and now U.S. Pat.No. 5,733,028, and U.S. application Ser. No. 08/589,105, filed Jan. 23,1996 and now U.S. Pat. No. 5,773,819, both of which are incorporatedherein by reference.

An alternative embodiment of an occluded and baffled emitter is shown inFIGS. 27A and 27B. An elongated lamp L, e.g., a minifluorescent lamp, islocated on the underside 24 of the mask M, between two closely spacedbaffles 41. Electrical power for the lamp is supplied on power leadsthat extend through a passageway formed in the base 18. The height ofthe baffles 41 exceeds that of the lamp L, such that the lamp L is notvisible from the side of the emitter.

In view of the foregoing, it can be seen that constructive occlusion canrender the distributor R and the detector T to provide tailoredradiation and detection profiles. When desired, constructive occlusioncan enhance the operation and function of the distributor R and thedetector T with respect to radiation in the horizon district, or evenrender the distributor R and the detector T to be substantiallyuniformly omnidirectional over a hemispheric area. The profiles of thedistributor R and the detector T can be further enhanced with the aid ofthe baffle. With determinative sizing and positioning of the mask and/orbaffle, the distributor R can be occluded in a manner that enables it todistribute uniform intensity in almost all directions and the detector Tcan be occluded in a manner that enables it to respond uniformly tointensity in almost all directions. The system advantageously appliesthese concepts. However, where the distributor R and the detector T havebeen rendered omnidirectional, the system uses a head module H that is acombination of an omnidirectional device with a partitioned device thatoperates with axial resolution.

In order to obtain directional (or angular) data in tracking areflector, the system employs a head module H that includes at least apartitioned distributor PR with a nonpartitioned detector T, or at leasta partitioned detector PT with a nonpartitioned distributor R, where thepartitioned devices operate with resolution about at least one axis. Inparticular, the system enables the generation and/or detection ofintensity variations between different sections that are indicative of adirection along which the reflector RR1 is positioned. As a feature ofthe present invention, the partitioned devices function and operate in amanner that allows the system to remain relatively simple electronicallyand structurally, and inexpensive.

Generally speaking, where a radiation or detection surface LS as shownin FIGS. 3A and 3B is utilized in the head module H, without the cavity16, the baffle 41 effectively divides or partitions the surface LSand/or a region between the mask M and the surface LS into sections inrendering a directional distributor or directional detector. In thisregard, as explained below in further detail, the light source providingthe radiation surface LS (or the detector providing the detectionsurface LS) is then configured to enable distinct radiation from (ordistinguish between distinct incidental radiation on) each of thesections created by the baffle 41.

Where the radiation surface or detection surface is provided by thecavity 16 and the aperture 22, such as in the distributor R and detectorT described above, the baffle 41 is modified or extended a baffle 51 todivide or partition the region into the sections that are now inclusiveof a volume substantially between the cavity 16 and the mask M. In orderthat the partitioned distributor (or detector) be able to enabledistinct radiation from (or distinguish between distinct incidentalradiation on) each of the sections, the point element 12 is replaced bya plurality of point elements, each of which is associated with adistinct section.

As shown in FIG. 9, the baffle 51 is similar to the baffle 41 of FIG.8A, but with the addition of dividers 53 which are substantiallyextended portions of the planar members 42. The dividers 53 areconfigured such that when the baffle 51 is placed between the mask M andthe cavity 16 (both represented by broken lines), the members 42 remainabove the aperture 22 while the dividers 53 extend below the apertureinto the cavity 16 and approach or abut the interior surface of thecavity 16. For example, where the cavity 16 is hemispherical orspherical, the dividers 53 have an curved profile 55.

Where the radiation or detection surface LS is present, a region Gbetween the surface LS and the mask M is divided by the baffle 41 intosections S_(i). Where the cavity 16 with the aperture 22 are utilized toprovide the surface LS, a region or volume G' between the cavity 16 andthe mask M is divided by the baffle 51 into the sections or subvolumesS_(i).

In one embodiment, the baffle 41 and 51 are substantially opaque, havinga thickness of approximately 3.0 mm. In an alternative embodiment, thebaffles 41 and 51 need not necessarily be opaque, provided that theysubstantially divide the region G into the sections, such that lightentering into each section substantially remains within that sectiononly.

Where the baffle 41 or 51 partitions or divides the region into foursections S_(A), S_(B), S_(C) and S_(D), the partitioned device hasresolution about two axes. Two axes of resolution can also be enabledwithin the system 10 where the baffle 41 or 51 partitions the regioninto three sections; however, it is believed that the calculations usedby the system to provide directional information would be more complex.Two axes of resolution are also enabled where baffle 41 or 51 dividesthe region into five or more sections. If only one axis of resolution isdesired, the baffle 41 or 51 is configured to partition the region intofewer sections, for example, two sections.

Where the baffle 51 provides four sections or quadrants (for resolutionabout two axes), an X/Y coordinate system may be superimposed on thebaffle 51, as illustrated, such that the cavity 16 is quartered inaccordance with the azimuth angle ρ being measured from the positive Xaxis. For purposes of better understanding this discussion, individualsections S_(A), S_(B), S_(C) and S_(D) may be defined as follows:

0<p<90=section B

90<p<180=section A

180<p<270=section D

270<p<360=section C

While the baffles 30, 41 and 51 all serve to increase the illuminationintensity at the horizon district (i.e., φ=90 or so), the extendedbaffle 51 divides the cavity 16 and renders the distributor R and thedetector T into partitioned distributor and detector PR and PT so thatthey provide resolution or distinguish direction about the X and Y axes.In particular, it is the baffle 51 which enables the partitioned devicesPR and PT to generate intensity variations in a manner that allows thesystem to ascertain at least directional data, if not positional datafor a reflector.

FIGS. 12A and 12B illustrate a partitioned device that is representativeof the partitioned distributor PR and the partitioned detector PT, usingthe cavity 16, the mask M and the baffle 51. The baffle 51 creates thesections, which includes lower sections below the aperture 22 within thecavity 16 and upper sections above the aperture 22 and below the mask M.As mentioned, a plurality of point elements 59 are used instead of thesingle point element 12 of FIG. 10 and each point element 59 isassociated with a distinct section. Each point element 59 may be mountedin a distinct section, in particular, a distinct upper section, on theunderside 24 of the mask M for the reasons previously discussed. Again,the point element 59 may represent light-conveying devices, as describedearlier.

Referring to FIG. 13, the system in one embodiment provides a headmodule H that includes a partitioned detector PT and distributor R. Thepartitioned detector PT may be configured as illustrated in FIGS. 12Aand 12B, and the distributor R may be configured as illustrated in FIG.10. As explained, each point sensor 59 of the partitioned detector PT isconfigured to generate electrical signals based on the light intensitydetected in the respective section. Where the point sensor 59 is aphotodiode, the photodiode has a relatively small responsive area ofapproximately 0.8 square millimeters and a noise equivalent power (NEP)of approximately 6×10⁻¹⁵ Watts/(Hertz)⁰.5. A photodiode with a smallresponsive area has two significant advantages: (i) it generally has lownoise characteristics; and (ii) the greater efficiency of the system(i.e., a decrease in the ratio of sensor size to cavity size meansgreater sensitivity). Using these photodiodes, the partitioned lightdetector's efficiency nears its asymptotic state with a cavity havingapproximately a 1.0 inch diameter or width.

As shown in FIG. 13, intensity variations detected by each of the pointsensors in the partitioned detector PT of the head module H is processedby a processor 49 (a representative circuit 67 thereof being shown indetail in FIG. 15) for display on an oscilloscope 64. The circuit 67 isequivalent to the circuit suggested by a manufacturer of photodiodes,namely, United Detector Technologies (UDT) Sensors, Inc., of Hawthorne,California, for use with its quad-cell photodiodes. Others circuits(analog or digital) may be used.

Referring specifically to FIG. 12B, the sections S_(A) S_(B) S_(C) andS_(D) created by the baffle 51 are arranged clockwise, when viewing downon the partitioned detector PT (see FIG. 13). Note that this arrangementcoincides with the sections shown in a conceptual representation in FIG.14, in that the normal extends outwardly from the horizon (or X/Y) planeinto the hemispheric area over the partitioned detector T.

Referring specifically to FIG. 15, the cathodes of the photodiodes areall connected to a common ground terminal. The anodes of the respectivephotodiodes are each connected to the respective current-to-voltageamplifier 50. The voltages are then summed and/or subtracted by one ofthree amplifiers 52, 54 and 57. The first amplifier 52 outputs a signalwhich is the sum of the signals from all four sections S_(A), S_(B),S_(C) and S_(D). The second amplifier 54 sums the signals from thesections B and C, and subtracts the sum of the signals from sections Aand D. The second amplifier's output signal is then divided by the firstamplifier's output signal by a divider 58 that provides and X outputsignal. A third amplifier 57 sums the signals from the sections A and B,and subtracts the sum of the signals from the sections C and D. Thethird amplifier's output signal is then divided by the first amplifier'soutput signal by a divider 60 that provides a Y output signal. Asuitable divider is the DIV100 manufactured and sold by Burr-Brown® ofTucson, Ariz.

The relationship between the X and Y output signals and the sectionsignals is given by the following formulas:

    X=[(B+C)-(A+D)]/(A+B+C+D)                                  Eqn. 1

    Y=[(A+B)-(C+D)]/(A+B+C+D)                                  Eqn. 2

It is understood by one of ordinary skill in the art that Equations 1and 2 may be varied so long as the configuration of the sections S_(A),S_(B), S_(C) and S_(D) is consistent therewith.

The X and Y output signals are fed to the oscilloscope 64 (FIG. 13). TheX output signal is connected to the display's horizontal sweep inputterminal and the Y output signal is connected to the oscilloscope'svertical sweep input terminal. It is understood by one of ordinary skillin the art that the signals X and Y are not necessarily defined within aCartesian coordinate system. A spot 66 on the oscilloscope 64 indicatesthe azimuth ρ and elevation φ position of the reflector. For example,the spot 66 indicated on the oscilloscope 64 is representative of aretro reflector positioned relative to the partitioned detector PT at anazimuth of about 45 degrees and an elevation of about 45 degrees. As thereflector changes elevation, the radial distance of the spot 66 from thecenter of the oscilloscope 64 changes. As the reflector movesazimuthally about the head module H, the spot 66 will trace a path aboutthe center of the oscilloscope 64.

A grid conceptually representative of the coordinate system for the Xand Y output signals is illustrated in FIG. 14. The azimuth (ρ) angle,taking into account the appropriate section (with the appropriatelydefined positive or negative values) for the reflector RR1 can becalculated from the X and Y output signals using the following formula:

    ρ=tan.sup.-1 (Y/X)                                     Eqn. 3

The elevation φ is related to the radial distance or length L from thecenter of the oscilloscope 64 to the spot 66 (FIG. 13). This radialdistance L is calculated from the X and Y output signals using thefollowing formula:

    L=(X.sup.2 +Y.sup.2)                                       Eqn. 4

The actual elevation associated with the calculated azimuth p and radiallength L is a complex function of the detector geometry. Accordingly, alook-up table given in Appendix A is used to correlate the azimuth ρ andthe length L, to the elevation, as follows. Note, however, that thetable provides the elevation angle in terms of Θ where Θ=90-φ.

    Θ={ρ,L; Table}                                   Eqn. 5

FIG. 14 illustrates conceptually the relationship set forth in AppendixA between the azimuth ρ, the radial length L, and the elevation Θ of aretro reflector detected at the azimuth angle ρ=30. In particular, ifthe reflector is at an elevation of Θ=10 (i.e., near the horizon), thespot 64 will be approximately 0.89 unit length L from the center of theoscilloscope 64. If the reflector moves to an elevation of Θ=80, thespot 64 will appear to closer to the center, with a reduced unit lengthL of approximately 0.76 from the center. Note that so long as the retroreflector remains at an azimuth of ρ=30, the spot will also remain at anazimuth of ρ=30 on the oscilloscope 64, changing only the length L fromthe center to reflect the change in elevation angle. If the retroreflector moves through different azimuths while remaining at the sameelevation, the spot 66 will travel on a somewhat rectangular path aroundthe center of the oscilloscope 64. Accordingly, the system using thetable in Appendix A provides a set of directional data (i.e., ρ, Θ) fora reflector being tracked.

It bears emphasis that the algorithm used in Appendix A is merely one ofnumerous algorithms that may be used by the system. The algorithm ofAppendix A is also one of many algorithms that allows the spot 66 toremain on the display regardless of the position of the object in thedetection zone Z. Moreover, it is understood by one of ordinary skill inthe art that directional data may provided by the system 10 through theuse of analytic relationships (e.g., polynomial equations), as opposedto the described embodiment using the look-up table of Appendix A.

In view of the foregoing, it can be seen that the partitioned lightdetector PT of the present invention provides at least directionalinformation in the form of a set of azimuth and elevation coordinates(ρ, Θ) for a given retro reflector. A partitioned detector embodyingfeatures of the present invention is disclosed in U.S. application Ser.No. 08/589,104, filed Jan. 23, 1996, which is incorporated herein byreference and now U.S. Pat. No. 5,705,804.

As an alternative embodiment of the partitioned devices in general, twopartitioned devices PD₁ and PD₂ (either both distributors or bothdetectors) may be placed back-to-back as shown in FIG. 28, to providespherical coverage that results from the two opposing hemispheric areaof the two devices.

While the embodiment described above uses a head module having apartitioned detector with a nonpartitioned, omnidirectional distributor,the system may also use a partitioned detector with other conventionallight sources under different conditions. For example, an ordinary broadband light bulb can be used where the detection zone is free from othertypes of illumination. Fluorescent light sources that flicker can alsobe used. A suitable fluorescent light bulb is the "Mini Fluorescent"(TM), Model BF659 in white color, made by JKL Components Corp. ofPacoima, Calif. Although conventional light sources will likely providea nonuniform radiation profile in the detection zone Z (the profilebeing particularly deficient at angles of φ at or near the horizonrelative to the light source), the system will function adequately forthose areas substantially normal to and outside the horizon district ofthe light source. The use of the distributor R instead of an ordinarylight source expands the operative zone of the system into a hemisphericarea over the distributor R, including the horizon district of thedistributor R.

In order to track multiple retro reflectors RR_(i) simultaneously withthe foregoing embodiment (see FIG. 1), that is, to provide additionalsets of directional data (ρ_(i), φ_(i)) for additional retro reflectors(whether affixed to additional objects, or to different locations on thesame object), the system necessarily distinguishes between signalsattributable to distinct retro reflectors. In this regard, it is notedthat the term "simultaneously" is used figuratively, and not necessarilyliterally, in that processing of data for multiple reflectors by thesystem may occur serially and not in parallel. Parallel processing maybe accomplished with additional processors.

The system 10 distinguishes between multiple reflectors by usingspectrally-selective sensors. In particular, where the light emittedfrom the distributor R is broad band light, reflectors of differentspectral characteristics are provided, along with a corresponding set ofspectrally-responsive point sensors (e.g., photodiodes equipped withspectrally-selective filters) for each additional reflector beingtracked. With the corresponding set of point sensors tracking its"assigned" retro reflector, the system is capable of tracking multipleretro reflectors and distinguishing between the intensities variationscollected for different reflectors.

Referring to FIG. 17, multiple sets of spectrally-selective pointsensors 71 and 72 (with frequencies responses of λ₁ and λ₂,respectively) may all be housed in a single partitioned detector PT. Inparticular, the sets 71 and 72 may be arranged such that each sectionbelow the mask M is occupied by one sensor from a given set. Thepartitioned detector PT of FIG. 17 can therefore detect at least tworeflectors with frequency spectrums similar to λ₁ and λ₂. The reflectorsmay each be affixed to different objects, or the reflectors may all beaffixed to a single (substantially rigid) object to track itsorientation.

In general, it is noted that the frequencies or spectral characteristicsof the electronics described herein are not specific wavelengths, butrather denote ranges of wavelengths. The responses from the sensor sets71 and 72 are used in equations herein to determine the position of thecorresponding reflectors. In general, the spectral characteristics ofthe reflectors need not be identical to the response characteristic ofits "assigned" sensors, though performance of the system 10 is improvedif they have similar characteristics.

If a third reflector is to be tracked, a third set of correspondingspectrally-responsive sensors with frequency spectrum λ₄ may be added tothe partitioned detector PT of the head module H. In the alternative, anadditional head module H_(n) with simply a partitioned detector PT_(n)may be added and used in conjunction with the head module H withoutrequiring reconfiguration of the latter. It can be seen in general thatadditional sets of sensors for detecting additional reflectors may behoused in the partitioned detector of an existing head module, or inseparate and distinct partitioned detectors T_(i). As shown in FIGS. 22Aand 22B, four separate and distinct partitioned detectors PT_(A),PT_(B), PT_(C) and PT_(D) are conveniently mounted on a single platformP, where each partitioned detector houses one set of sensor sets S_(A),S_(B), S_(C) and S_(D).

It has been noted that a single partitioned detector PT of the abovedescription can provide one set of directional data (ρ₁, Θ₁) for a givenreflector. Referring back to FIG. 1, where it is desirable to ascertainthe position of a reflector in three dimensions (along three axes), thesystem uses at least one additional partitioned light detector PT₂ toprovide a second set of directional coordinates ρ₂ and Θ₂, which whenprocessed with the first directional coordinates ρ₂ and Θ₂, provides allthree coordinates for the reflector. The relative positions of thepartitioned detectors PT and PT₂ to each other is made known to thesystem so that it can cross-reference the signals from both partitioneddetectors to ascertain all three coordinates for a reflector from twosets of directional data.

In view of the foregoing, it can be seen that to ascertain all sixcoordinates for an object (that is, position and rotationalorientation), the system uses at least three reflectors and twopartitioned detectors. However, detection of all six degrees of movementof an object is not always desirable or required, and the system 10 canbe configured appropriately.

Referring to FIG. 1, where a second partitioned detector PT₂ is used, itis part of a second head module H₂ providing a second distributor R₂.The second distributor R₂ provides the light that is detected by thesecond partitioned detector. With the two head modules H₁ and H₂ andtheir relative positions known, the system can cross-reference therespective sets of directional data for any one reflector tracking themovement of that reflector in three coordinates. A divider or aseparating wall (not shown) may be situated between the head modules H₁and H₂ to prevent interference by the respective light distributors.Alternatively, the radiation from the respective distributors may bepulsed or flickered at different frequencies, e.g., 100 Hz and 130 Hz.

As shown in FIG. 1, broad band light is emitted throughout the detectionzone Z. Where the detection zone Z contains extraneous objects such asfurniture or walls with extensive reflective surfaces, light isreflected not only off the reflectors, but off these surfaces as well.Any light detected by the head module not attributable to the reflectorcontributes to the background energy which may significantly limit theperformance of the system 10. However, because this background energy(also known as background or self illumination) is not a noise source,but a background source, its effects can be compensated. Where multiplesensors of different spectral responsiveness are used, this backgroundsource can be reduced if not eliminated.

Referring back to the embodiment shown in FIG. 17, multiple sensors ofdifferent spectral responsiveness are used, that is, sensor sets 71 and72 responsive to frequencies λ₁ and λ₂ are used to track twocorresponding reflectors, as previously described. To compensate forbackground illumination, a third set of sensors 73 is provided. Thefrequency response of the third set 73 is selected to be responsive toall wavelengths in the area of the spectrum near the frequencies λ₁ andλ₂ so that it can act as a background nulling detector. To demonstratethe effects of background illumination, responses r₁ and r₂ of the firstand second sets of sensors, after subtraction of the background energy,are given by:

    r=K.sup.-1 R                                               Eqn. 6

Where: ##EQU1## And R₁ is the sensor response before backgroundcorrection and K_(ii) are constants of correction.

As the background level increases, the dynamic range requirements of theelectronics increase. To calculate the magnitude of the selfillumination, integrating sphere models are used. The background light Breflecting off the walls of a room back to the partitioned detector PTis given by: ##EQU2##

Where A_(e) is the acceptance area or aperture of the partitioneddetector PT, A_(w) is the area of the room walls, and W_(r) is the roomwall reflectance.

The signal from the retro reflector is given by:

    S=Lr*Pr                                                    Eqn. 8

Where: ##EQU3##

and Θ' is the divergent angle of the retro reflector, as previouslydefined, A_(r) is the area of the retro reflector, and Dr is thedistance to the retro reflector.

Table 1 below lists signal to background and A/D requirements forselected conditions using a 1" diameter retro reflector, where Rs is theroom size in feet, D_(r) is distance to the retro reflector in feet, andW_(r) is the wall reflectance. A smaller signal to background required alarger Analog to Digital (A/D) converter. For a system requiring a 1°resolution, a 20 bit A/D is sufficient or a signal to background of0.013. 20 bit A/Ds are readily available and inexpensive.

    ______________________________________                                        Condition       Signal Background                                             Rs  D.sub.r                                                                             W.sub.r  in Watts                                                                            in Watts  S/B Ratio                                                                            A/D                                 ______________________________________                                        Required                                                                      12' 12'   75%      2.9E-6                                                                              2.2E-4    1.3E-2 20                                  bit                                                                           12'  6'   75%        4.6E-5                                                                               2.2E-4   2.1E-1                                                                               14                                bit                                                                           12'  6'   95%        4.6E-5                                                                               1.4E-3    3.3E-2                                                                             18                                 bit                                                                           12'  10'  10%       2.0E-6                                                                                8.1E-6    3.5E-1                                                                                14                              bit                                                                           24'  24'  75%       1.8E-7                                                                                5.5E-5    3.3E-3                                                                                24                              bit                                                                           24'  12'  75%       2.9E-6                                                                                5.5E-5    5.3E-2                                                                                18                              bit                                                                           24'  12'  95%       2.9E-6                                                                                3.5E-4    8.7E-3                                                                              18                                bit                                                                           24'  24'  10%       1.8E-7                                                                                2.0E-6    8.9E-2                                                                               16                               bit                                                                           ______________________________________                                    

A head module H including a partitioned detector PT and a nonpartitioneddistributor R is shown in FIG. 16. The partitioned detector PT and thedistributor R of this head module each has its own cavity. A cavity16_(R), mask M_(R) and baffle 41 are provided for the distributor R, anda separate cavity 16_(PT), mask M_(PT) and baffle 51 are provided forthe partitioned detector PT, albeit the cavity 16_(R) is actuallyconfigured in the mask M_(PT) of the partitioned detector PT. Configuredin this manner, the partitioned detector PT and the distributor Rfunction without significant disturbance to the other. The distributor Rdistributes light into the hemispheric area over the head module H,including the horizon district around the distributor R (and the headmodule H). Any light reflected by a reflector in the hemispheric area isdetected by the partitioned detector PT, even if reflected from thehorizon district. Equipped with the extended baffle 51, the partitioneddetector PT is able to detect intensity variations between the sectionsto enable the system to provide a set of directional data of ρ and Θ foreach reflector.

The head module with separate cavities may be the simplest and leastcostly to manufacture. The separate cavity feature enables the use ofcontinuous or slowly oscillating illumination and relatively largerlight sources. This embodiment is advantageous in that it avoids the useof moving components and imposes relatively slow response requirementson the electronics of the system.

As a variation on the head module, reference is made to FIGS. 18A and18B. A single cavity 16 is provided and shared by a distributor R and apartitioned detector PT. One mask M and one extended baffle 51 are usedin this embodiment. The partitioned detector PT uses three sets ofsensors 71, 72 and 73 to detect two reflectors (the third set 73 forbackground illumination). Since the distributor R shares a cavity 16that has been divided by the baffle 51, the distributor R uses aplurality of emitters 74, one for each section under the mask M. As afurther variation on the head module, the emitters 74 can be broad bandpulse emitters. By measuring the time elapsed for the pulses to returnto the head module H, the system can obtain a range R of the reflectorfrom the head module H, by: ##EQU4## where c is the speed oflight=3.998×10⁸ m/sec.

A pulse leading edge width or rise time of approximately 1 nanosecondwould give a resolution of approximately 0.15 m or 5.8". As opposed torequiring an electronics response time of approximately milliseconds(10⁻³ sec) as in the separate cavity embodiment discussed above, thisembodiment typically requires an electronics response time ofapproximately nanoseconds (10⁻⁹ sec). With the elapsed time measurementproviding actual range data (as opposed to the representative length Ldiscussed above), the system using this variation of the head module isable to provide all three coordinates of a reflector without using asecond head module. In order to track rotational movement, the system 10needs only two additional retro reflectors, both of which are alsotracked by the head module H. It is understood by one of ordinary skillin the art that the "time of flight" variation is not limited to thesingle-cavity embodiment, but may also be used in the separate-cavityembodiment, described earlier.

While background illumination can be contending factor in theembodiments described above, the system can be configured to generateminimal background illumination, as discussed below.

Referring to FIGS. 19A and 19B, the light distributor R of the headmodule H is replaced by a scanning light mechanism 76. The scanninglight mechanism 76 includes a plurality of scanning mirrors 78 whosemovement are guided by galvanometers 80. Light from a point light source82 is redirected by the mirrors 78 to form a scan beam 84 that sweepsthe zone Z. Other types of optical scanners exist, such as rotatingwedges and rotating reflectors, and may be used in the system.

The scanning beam 84 may be approximately 10 degrees wide. The beam orits sweeping action is not timed or sequenced, but simply serves toilluminate a limited section or portion of the detection zone Z at agiven time. The partitioned detector PT is set with a detectionthreshold such that no position tracking is attempted by the system 10if the beam strikes no reflector. When the beam 84 does illuminate areflector, the optical intensity striking the partitioned detector PTexceeds the threshold and the system 10 processes the intensityvariations detected by the sets of sensors.

The partitioned detector PT of this embodiment is split into symmetricalcomponents. As shown in FIG. 19B, the partitioned light detector PT isdivided into two portions PT_(a) and PT_(b), between which the scanningmechanism 76 is positioned. By splitting the partitioned detector PT,shadowing by the scanning mechanism 76 is significantly reduced and thepartitioned detector PT remains capable of detecting radiation about twoaxes of resolution. The head module H of this embodiment provides only aone set of directional data (azimuth and elevation) for a reflector.

Because the scan beam 84 illuminates only a section of the zone Z at agiven time, this embodiment has a distinct advantage of lower backgroundillumination and may thus be preferred for applications with a largenumber of reflectors. Without the need to perform backgroundsubtraction, the system of this embodiment can readily track multipleretro reflectors using a small number of filter sensor combinationswhich cooperatively perform a "color" analysis on the signals detected.In fact, the system can be configured to distinguish between a verylarge number (i.e. thousands) of spectrally-distinguishable reflectors,using as little as two or three sets of sensors. Of course, it isunderstood by one of ordinary skill in the art that a larger number ofsets can be used.

The color analysis performed by the system is much like that used by thehuman eye to detect color. The eye using only three detectors (or"cones") is able to distinguish between a variety of colors.Correspondingly, the system using only three sets ofspectrally-selective sensors 91, 92 and 93 as shown in FIG. 19B, candistinguish between a variety of spectrally-distinguishable reflectors.

If the scan beam 84 happens to strike multiple reflectorssimultaneously, the system can process the signals in a manner much likethat used for compensating background illumination, described above.

The system also uses color analysis in another embodiment. Referring toFIGS. 20A and 20B, the system 10 includes a head module H having anonpartitioned detector T and a partitioned distributor PR, withseparate cavities 16_(T) and 16_(PR), separate masks M_(T) and M_(PR), abaffle 41 and a cavity dividing baffle 51. The partitioned distributorPR is equipped with different color lamps C_(A), C_(B), C_(D) and C_(D)to radiate a different color (i.e., radiation of a different wavelength)from each section. The resulting color mix reflected by a reflector isdetected by the detector T using three single point sensors 95. Thesystem analyzes the color mix detected by the detector T to obtain a setof directional data (azimuth and elevation) for that reflector.

Additional reflectors may be tracked where the reflectors are equippedwith shutters, such as LCD shutters. This allows this embodiment of thesystem 10 to distinguish between multiple points, e.g., by timing theshutters so that the light data transmitted by each reflector istransmitted as pulse data at different pulse rates.

Still referring to FIGS. 20A and 20B, the partitioned distributor PR inan alternative embodiment may be equipped with emitters of differenttemporal frequency. That is, each section of the partitioned distributorPR may house a lamp or emitter that flickers at a distinct frequency sothat the nonpartitioned detector T is able to distinguish between lightfrom each lamp or emitter.

While the above embodiments of the present invention are configured asoptically-passive systems, the invention may also be configured as anoptically-active system. Referring to FIG. 21, active light sources 88₁and 88₂, such as LEDs, replace the optically-passive reflectors (therebyobviating the use of a light source or light distributors). With onepartitioned detector PT₁, directional data for each of the sources 88₁and 88₂ is obtained. With two partitioned detectors PT₁ and PT₂,positional data in all three coordinates for both of sources 88₁ and 88₂obtained. The active light sources are distinguishable from each otherby emitting distinguishable colors, or oscillating at distinguishablefrequencies.

As another optically-active embodiment of the present invention, thesystem 10 includes the partitioned distributor PR of FIG. 20B, and thepartitioned detector PT of FIG. 17. The partitioned distributor PR withthe color lamps C_(A), C_(B), C_(D) and C_(D), or emitters of differenttemporal frequencies, as described above, may itself be mounted on orotherwise attached to the object being tracked. The resulting color mixfrom the partitioned distributor PR is detected by the sets of sensors71, 72 and 73 of the partitioned detector PT of FIG. 17, which nowperform a color analysis on the color mix to provide a set ofdirectional data for the object relative to the partitioned detector PT.

It is noted that the accuracy of the directional performance of thelight distributor and/or light detector can be empirically optimizedusing a variety of parameters. For example, the height, relativediameter, thickness, and reflectivity of the mask, the width andreflectivity of the shoulders, the height and reflectivity of the baffleassembly, the shape and reflectivity of the cavity, and the photodiode'sdiameter, all affect the light detector's directional response.Conversely, the distributor's and/or the detector's directionalperformance can be tailored to be nonuniform, if desired, by varyingspecific parameters. For example, decreasing the distance between themask and the aperture will decrease the spherical profile of thedetector's response, while increasing the detector's "on-axis"efficiency. When the mask is placed in the plane of the aperture, thedetector's "on-axis" efficiency improves to about 90%, compared to about40% with a mask above the aperture, but its response profile isnarrowed, rendering a less uniform detection profile. The lightdetector's spectral response can also be tailored by using spectrallyselective paint on the diffusely reflective surfaces or a filtered domeor cover.

Referring back to FIG. 1, for all the embodiments discussed above, thesignals representative of the position of the object tracked can beconverted into video signals to drive a video monitor displaying theposition or movement of the object. The reflectors may be removablyaffixed to the object, such that they can be readily transferred betweendifferent game equipment, such as game swords or game boxing gloves.

As further embodiments of the system, an occluded distributor ordetector 98 may be configured to provide to a radiation or detectionprofile that is substantially uniform over a spherical area. Asillustrated in FIGS. 23A, 23B, 23C, the occluded device includes atubular member 100 having a diffusely reflective interior surface 102defining an interior volume or cavity 104. The tubular member 100 isillustrated with a cylindrical configuration; however, the member 100need not have a circular cross section. The tubular member 100 has openends 106 providing two apertures 108 from which radiation may enter intoor exit from the cavity 104. The apertures 108 are constructivelyoccluded with masks M and the cavity 104 is divided by a planar baffle110 to form two half volumes V₁ and V₂ inside the tubular member 100. Apoint element 112 is housed in each half volume, at a midlocation alongthe length of the member 100. Accordingly, the device 98 is operationalwith respect to one axis of resolution.

Where the point element 112 is an emitter, radiation is emitted fromeach end 106 of the occluded device 98 with a tailored distributionprofile over the aperture 108. Correspondingly, where the point element112 is a detector, the occluded device 98 detects radiation with atailored detection profile over the aperture 108.

For substantially spherical coverage, a second occluded tubular device114 is provided. The second device 114 is structured similarly to thefirst device 98 and thus like numerals refer to like elements. Thesecond device 114 is positioned orthogonally to the device such that itsapertures 108 are offset substantially 90 degrees from the apertures 108of the first device. As the device 114 is also divided by the planarbaffle 110, the two devices together are operational with respect to twoaxes of resolution.

Additionally, the concept of constructed occlusion can be accomplishedby reconfiguring the substantially Lambertian surface into multipledistinct surfaces which can alternatively occlude each other. Asillustrated in FIGS. 24A--24D, an annular or ring structure isillustrated, having an opening or otherwise nonoptical area 122 throughwhich an axis or boresight 124 can be drawn. It is understood by one ofordinary skill in the art that the area 122 may alternatively benon-reflective and/or nontransmissive. The axis 124 is substantiallynormal to a plane within which the ring structure is confined. Theelevation angle φ is defined as the angle from the boresight 124.

The ring structure provides two distinct surfaces that can eitherradiate or detect light. In particular, the ring structure includes afirst annular structure 126 that provides a first surface 128 that facesinwardly toward the area 122. The ring structure also includes a secondannular structure 130 (shown in exploded view in broken lines in FIG.24A) that provides a second surface 132. The second structure 130 fitswithin the first structure 126 and may reside at any predetermined depthwithin the first structure 126 as shown by the arrow 123. Fitted insidethe first structure 16, the second structure 130 effectively projectsangularly from the first structure 126 with the surfaces 128 and 132being angularly offset from each other. In one embodiment, the first andsecond surfaces are normal to each other, with the second surface 132being substantially parallel with the plane of the area 122 and thussubstantially normal to the boresight 124. While this may offer thesimplest configuration, the first and second surfaces 128 and 132 neednot be normal to each other so long as they can occlude each other asdesired and any angle therebetween is known. Typically mutual selectiveocclusion is afforded if the structures 126 and 130 are nonparallel.Moreover, the second surface 132 need not be normal to the boresight 124so long as any angle therebetween is known.

Referring to FIG. 24C, the second structure 130 is situated at a lowerdepth within the first structure 126. However, as mentioned, the secondstructure 130 can also be situated at a midline of the first structure126, as shown in FIGS. 25A-25C. Depending on dimensions 134 of the firststructure 126 and 136 of the second structure 130, and a spacing 137 thefirst and second structures, the cross section K can be keptsubstantially constant for most angles of φ. It can be seen that for theangle of φ approaching the horizon as shown in FIG. 24C, the first andsecond left surfaces 128_(L) and 130_(L) are unoccluded, whereas thefirst and second right surfaces are occluded, to provide the total crosssection K. Where the angle of φ is substantially zero, only the secondsurfaces 130_(R) and 130_(L) are unoccluded, whereas both the firstsurfaces 128_(R) and 128_(L) are effectively occluded to provide thetotal cross section K.

Accordingly, the first and second structures 126 and 130 eachconstructively occludes the surfaces of the other for different anglesof φ, keeping the cross section area K relatively constant to provide arelatively uniform radiation or detection profile. Like the occludeddevices described earlier, the ring structure is substantiallyomnidirectional for either radiation purposes or detection purposes.

Where the second structure 130 is at a mid-depth in the first structure126, the cross section K also remains relatively constant for differentangles of φ. As shown in FIG. 25C, the left second structure 130_(L)constructively occludes or masks a portion 138 of the left first surface128_(L), while the right first structure 126_(R) completely occludes theright second surface 132_(R). Accordingly, the first and secondstructures 126 and 130 each constructively occludes the surfaces of theother for different angles of φ, keeping the cross section area Krelatively constant to provide a relatively uniform radiation ordetection profile. In FIGS. 24A-24C and 25A-25C, the structure 120 isconfigured as a circular ring; however, it can be configured in anyshape, provided the opening or nonoptical area 122 is present.

Referring to FIGS. 25A-25C only, to provide at least one axis ofresolution in rendering the structure 120 directional in one coordinate,the structure 120 is divided into at least two discrete portions orsegments 150. The disclosed structure 120 of is divided into foursegments 150a, 150b, 150c and 150d, as best shown in FIG. 25B, toprovide two axes of resolution rendering the structure 120 directionalin two coordinates, in the manner described earlier.

In FIG. 25A, the segment 150d is shown partially broken away to revealthe cross section view of segment 150a which is representative of allthe segments 150a-150d. The division in the structure 120 is preferably,but not necessarily, made so that each segment provides substantiallysymmetrical and equal surfaces 128 and 132. In this embodiment, thesegments 150a-150d are insulated from each other by gaps 152 filled withair or insulating material such that each segment is unaffected by theradiation or detection function of the others.

With the structure 120 as a radiator or emitter, each of the segmentscan radiate distinguishable radiation. With the structure 120 as adetector, the structure 120 is electrically configured such that eachsegment 150a-150d can generate signals representative of the radiationincident on the respective segment.

As a further variation, the structure 120 can be constructed out ofsilica, or a calorimetric substance that is sensitive to infraredradiation. In that regard, the first and second surfaces 128 and 132 maybe rendered a dark shade or color such that infrared radiation incidenton the structure 120 is readily detected.

Where spherical coverage is desired or appropriate, two ring structures120' and 120" may be used in a back-to-back configuration as shown inFIGS. 29A and 29B. In the illustrated embodiment, a singlenon-reflective and non-transmissive member 122' is provided between thetwo structures 120' and 120" and each of the structures 120' and 120" isdivided into the segments 150a'-150d' and 150a"-140d", respectively, toprovide resolution about two axes (the segments 150d' and 150d" are notshown and the segments 150c' and 150c" are shown partially broken away).

In the orientation of FIGS. 29A and 29B, it can be seen that the ringstructure 120' provides "top" hemispherical coverage and the ringstructure 120" provides "bottom" hemispherical coverage, which togetherprovide the spherical coverage.

Referring to FIGS. 26A and 26B, another embodiment of a constructivelyoccluded, directional optical device 160 is illustrated. The device 160includes a base 162 constructed much like the base 18 earlier described,except that the base 162 contains four spherical cavities 164a, 164b,164c and 164d, all of which are constructively occluded by a mask 166configured from an upper portion 168 of the base 162. Each of thespherical cavities has a surface or aperture 167 that is occluded by themask 166 so that the cross section area K remains substantially constantfor most angles of φ. A plurality of optical point elements 180, eitheremitters or detectors, are provided, with each being associated with adistinct cavity.

Described another way, it can be seen that the four spherical cavities164a-164d jointly form a larger cavity (delineated in FIG. 26B by brokenline segments 169) which has been partitioned by a core section 170 ofthe base situated between the four spherical cavities, on which the maskM is supported. The core section 170 acts much like the baffle 51described earlier in enabling the radiation in each cavity 164a-164d toremain therein. With the four spherical cavities, the device offers twoaxes of resolution, as described earlier.

As mentioned, the radiation or detection profile of an occluded devicein accordance with a feature of the present invention can be tailored asdesired or needed. As an example of an occluded device providing anonuniform, tailored radiation or detection profile, reference is madeto FIGS. 30A-30C. An occluded device 200 is shown, having a diffuselyreflective cavity 202, which in the illustrated embodiment, iscylindrical with a constant circular cross-section area 204. An aperture206 of the cavity 202 provides a radiation or detection surface 208. Theoccluded device 200 includes a diffusely reflective mask M.

In this embodiment, the mask M has a width W_(M) that is greater than awidth W_(A) of the aperture 206 and is positioned a distance D from thesurface 208 or aperture 206. For example, the width W_(M) may beapproximately 0.265", the width W_(A) may be approximately 0.250", andthe distance D may be 0.075". In this embodiment, the mask M overreachesand extends beyond the aperture 206. With the mask M so configured, itcan be seen that a cross section area K_(H) for angles of φ in thehorizon district is substantially at a maximum, and is reduced to across section area K_(E) as the angle φ is reduced. In fact, for anglesof φ approaching zero (i.e., normal to the aperture 206), the crosssection K is zero, as the mask M completely occludes the aperture 206.Accordingly, the device 200 has reduced function in the elevation anglesover the hemispheric area or sector which the device 200 faces. Butbecause the cross section area K_(H) is substantially at a maximum andremains substantially at the maximum for all azimuth angles (i.e.,0<p<360), the device 200 is rendered an azimuthal device having aradiation or detection profile that is substantially uniform in theazimuth direction at or near the horizon district of the device 200.

To provide resolution about at least one axis in the azimuth direction,the device includes a diffusely reflective baffle 214 that partitions ordivides the cavity 202 into the sections S. Referring specifically toembodiment of FIG. 30B, the baffle 214 preferably, but not necessarily,divides the cavity 202 into four section S_(A), S_(B), S_(C) and S_(D).As an emitter, the device 200 may then include four emitters 220_(A)-220_(D), each of which is housed in a distinct section. Much like thehemispherical partitioned distributor PT of FIGS. 20A and 20B, describedearlier, the emitters 220 can be lamps of different colors or differenttemporal frequencies, except that the device 200 operates azimuthally,as opposed to hemispherically.

As a detector, the azimuthal device 200 may include a plurality ofdetectors (also represented by reference numerals 220) in associationwith the sectors. For the device 200 to locate the azimuthal angle ofincoming light over 360 degrees in its horizon district, the baffle 214is configured to partition the cavity 202 into at least the foursections S_(A), S_(B), S_(C) and S_(D), each of which houses a distinctemitter 220.

For the azimuthal device 200 to locate the azimuth angle of incominglight over 180 degrees in its horizon district, the baffle 214 isconfigured to partition the cavity 202 into at least three sections thatspan preferably, but not necessarily, 270 degrees. As shown in FIG. 30C,the three sections may be sections S_(A), S_(D) and S_(C), each with itsrespective detector 220. As a fourth detector 220 is not used in thisembodiment for detection coverage of 180 degrees, the "nonactive"section S_(B) is shown without a detector.

It is understood by one of ordinary skill in the art that the pluralityof sections and/or the plurality of optical elements 220 associated withthe sections S may be tailored or changed to meet the desired functionand operation of the device 200 as either a partitioned azimuthaldistributor or a partitioned azimuthal detector.

As a further example of tailoring the radiation or detection profile ofthe azimuthal device 200, the device 200 is shown in FIGS. 31A-31C wherethe width W_(M) of the mask M is substantially equal to the width W_(A)of the aperture 206. It can be seen that the cross section area K_(H)has remained substantially unchanged from that of FIGS. 30A-30C;however, cross section area K_(E) ' of FIG. 31A has increased over thearea K_(E) of FIG. 30A.

It is noted that the optical elements 220 of FIGS. 30A-30C arepositioned in the "bottom" of the cavity 202, whereas the opticalelements 220 of FIGS. 31A-31C are positioned on the "sides" of thecavity 202. In either instance, the sites of the elements 220 within thecavity 202 are selected so as to avoid "hot spots," as describedearlier, if "hot spots" are undesirable or disruptive. The embodiment ofFIGS. 30A-30C may be preferred for a floor-mounted azimuthal device andthe embodiment of FIGS. 31A-31C may be preferred for a wall-mountedazimuthal device.

Like the embodiments described above, the cavity 202, the mask M, and/orthe baffle 214 may be diffusely reflective, and the cavity 202 may beany shape, although the cylindrical shape is preferred in mostinstances. A protective cover 224 may also be provided.

It can be seen that the present invention provides a relatively simpleand cost effective system that can track the position of objects movingin a three-dimensional zone, without a large number of optical elementsor complex processing electronics. Although the foregoing discloses thepresently preferred embodiments of the present invention, it isunderstood that the those skilled in the art may make various changes tothe preferred embodiments shown and described without departing from thescope of the invention. Accordingly, the invention is defined only bythe following claims.

                  APPENDIX A                                                      ______________________________________                                        Azimuth=ATAN(y/x)*180/PI()+                                                   IF(x<0,180.0)+IF(AND(x>0,y<0),360,0)                                          Length=SQRT(x 2+y 2)                                                          Where                                                                         X=((b+c)-(a+d))/(a+b+c+d)                                                     y=((a+b)-(c+d))/(a+b+c+d)                                                     and a,b,c,d are quadrant responses                                            Lookup Table for QHD                                                          Azimuth         Length  Elevation                                             ______________________________________                                        0               1.0000  0                                                     0                      0.9640                                                                              10                                               0                      0.9345                                                                              20                                               0                      0.8853                                                                              30                                               0                      0.8304                                                                              40                                               0                      0.7945                                                                              50                                               0                      0.7364                                                                              60                                               0                      0.6894                                                                              70                                               0                      0.3913                                                                              80                                               0                      0.0000                                                                              90                                               10                    1.0154                                                                                0                                               10                    0.9663                                                                               10                                               10                    0.9381                                                                               20                                               10                    0.9151                                                                               30                                               10                    0.8871                                                                               40                                               10                    0.8701                                                                               50                                               10                    0.8498                                                                                60                                              10                    0.7762                                                                                70                                              10                    0.4191                                                                                80                                              10                    0.0000                                                                                90                                              20                    1.0642                                                                                0                                               20                    0.9320                                                                                10                                              20                    0.9017                                                                                20                                              20                    0.8712                                                                                30                                              20                    0.8620                                                                                40                                              20                    0.8290                                                                                50                                              20                    0.7970                                                                                60                                              20                    0.7253                                                                                70                                              20                    0.4896                                                                                80                                              20                    0.0000                                                                                90                                              30                    1.1547                                                                                0                                               30                   0.8983                                                                                  10                                             30                   0.8408                                                                                 20                                              30                   0.8306                                                                                 30                                              30                   0.8028                                                                                 40                                              30                   0.7943                                                                                 50                                              30                   0.7576                                                                                 60                                              30                   0.7031                                                                                 70                                              30                   0.5355                                                                                 80                                              30                   0.0000                                                                                 90                                              40                   1.3054                                                                                  0                                              40                   0.8784                                                                                 10                                              40                   0.8136                                                                                 20                                              40                    0.8122                                                                              30                                                40                    0.8090                                                                              40                                                40                    0.7492                                                                              50                                                40                    0.7307                                                                              60                                                40                    0.6978                                                                              70                                                40                    0.5904                                                                              80                                                40                    0.0000                                                                              90                                                50                    1.3054                                                                              0                                                 50                    0.8784                                                                              10                                                50                    0.8136                                                                              20                                                50                    0.8122                                                                              30                                                50                    0.8090                                                                              40                                                50                    0.7492                                                                              50                                                50                    0.7307                                                                              60                                                50                    0.6978                                                                              70                                                50                    0.5904                                                                              80                                                50                    0.0000                                                                              90                                                60                     1.1547                                                                             0                                                 60                     0.8983                                                                             10                                                60                   0.8408                                                                               20                                                60                   0.8306                                                                               30                                                60                   0.8028                                                                               40                                                60                   0.7943                                                                               50                                                60                   0.7576                                                                               60                                                60                   0.7031                                                                               70                                                60                   0.5355                                                                               80                                                60                   0.0000                                                                               90                                                70                   1.0642                                                                               0                                                 70                   0.9320                                                                               10                                                70                   0.9017                                                                               20                                                70                   0.8712                                                                               30                                                70                   0.8620                                                                               40                                                70                   0.8290                                                                               50                                                70                   0.7970                                                                               60                                                70                   0.7253                                                                               70                                                70                   0.4896                                                                               80                                                70                   0.0000                                                                               90                                                80                    1.0154                                                                             0                                                  80                   0.9663                                                                              10                                                 80                   0.9381                                                                              20                                                 80                   0.9151                                                                              30                                                 80                   0.8871                                                                              40                                                 80                   0.8701                                                                              50                                                 80                   0.8498                                                                              60                                                 80                   0.7762                                                                              70                                                 80                   0.4191                                                                              80                                                 80                    0.0000                                                                            90                                                  90                    1.0000                                                                             0                                                  90                    0.9640                                                                            10                                                  90                    0.9345                                                                            20                                                  90                    0.8853                                                                               30                                               90                    0.8304                                                                               40                                               90                    0.7945                                                                               50                                               90                    0.7364                                                                               60                                               90                   0.6894                                                                                70                                               90                   0.3913                                                                                80                                               90                   0.0000                                                                                90                                               100                  1.0154                                                                                 0                                               100                  0.9663                                                                                10                                               100                  0.9381                                                                                20                                               100                  0.9151                                                                                30                                               100                  0.8871                                                                                40                                               100                  0.8701                                                                                50                                               100                  0.8498                                                                                60                                               100                  0.7762                                                                                70                                               100                  0.4191                                                                                80                                               100                  0.0000                                                                                 90                                              110                   1.0642                                                                               0                                                110                   0.9320                                                                               10                                               110                   0.9017                                                                               20                                               110                   0.8712                                                                               30                                               110                   0.8620                                                                               40                                               110                   0.8290                                                                               50                                               110                   0.7970                                                                               60                                               110                   0.7253                                                                               70                                               110                   0.4896                                                                                80                                              110                   0.0000                                                                               90                                               120                   1.1547                                                                                0                                               120                   0.8983                                                                               10                                               120                  0.8408                                                                                20                                               120                  0.8306                                                                                30                                               120                  0.8028                                                                                 40                                              120                  0.7943                                                                                50                                               120                  0.7576                                                                                60                                               120                  0.7031                                                                                70                                               120                  0.5355                                                                                80                                               120                  0.0000                                                                                90                                               130                   1.3054                                                                               0                                                130                  0.8784                                                                                 10                                              130                  0.8136                                                                                 20                                              130                  0.8122                                                                                 30                                              130                   0.8090                                                                               40                                               130                   0.7492                                                                               50                                               130                   0.7307                                                                               60                                               130                   0.6978                                                                               70                                               130                   0.5904                                                                               80                                               130                   0.0000                                                                               90                                               140                   1.3054                                                                               0                                                140                   0.8784                                                                               10                                               140                   0.8136                                                                               20                                               140                   0.8122                                                                               30                                               140                   0.8090                                                                               40                                               140                   0.7492                                                                               50                                               140                   0.7307                                                                               60                                               140                   0.6978                                                                               70                                               140                   0.5904                                                                               80                                               140                   0.0000                                                                               90                                               150                   1.1547                                                                                0                                               150                   0.8983                                                                               10                                               150                   0.8408                                                                               20                                               150                   0.8306                                                                               30                                               150                   0.8028                                                                               40                                               150                   0.7943                                                                               50                                               150                   0.7576                                                                               60                                               150                   0.7031                                                                               70                                               150                   0.5355                                                                               80                                               150                   0.0000                                                                               90                                               160                    1.0642                                                                              0                                                160                   0.9320                                                                               10                                               160                    0.9017                                                                              20                                               160                   0.8712                                                                                30                                              160                   0.8620                                                                                40                                              160                   0.8290                                                                                50                                              160                   0.7970                                                                                60                                              160                   0.7253                                                                                70                                              160                   0.4896                                                                                80                                              160                   0.0000                                                                                90                                              170                   1.0154                                                                                0                                               170                   0.9663                                                                                10                                              170                   0.9381                                                                                20                                              170                   0.9151                                                                                30                                              170                   0.8871                                                                                40                                              170                   0.8701                                                                                50                                              170                   0.8498                                                                                60                                              170                   0.7762                                                                                70                                              170                   0.4191                                                                                80                                              170                   0.0000                                                                                90                                              180                   1.0000                                                                                 0                                              180                   0.9640                                                                               10                                               180                   0.9345                                                                               20                                               180                   0.8853                                                                               30                                               180                   0.8304                                                                               40                                               180                   0.7945                                                                               50                                               180                   0.7364                                                                               60                                               180                   0.6894                                                                               70                                               180                   0.3913                                                                               80                                               180                   0.0000                                                                               90                                               190                   1.0154                                                                               0                                                190                   0.9663                                                                               10                                               190                   0.9381                                                                               20                                               190                   0.9151                                                                               30                                               190                   0.8871                                                                               40                                               190                   0.8701                                                                               50                                               190                   0.8498                                                                               60                                               190                   0.7762                                                                               70                                               190                   0.4191                                                                               80                                               190                   0.0000                                                                               90                                               200                   1.0642                                                                               0                                                200                   0.9320                                                                               10                                               200                   0.9017                                                                               20                                               200                   0.8712                                                                               30                                               200                   0.8620                                                                               40                                               200                   0.8290                                                                               50                                               200                   0.7970                                                                               60                                               200                   0.7253                                                                               70                                               200                   0.4896                                                                               80                                               200                   0.0000                                                                               90                                               210                    1.1547                                                                             0                                                 210                    0.8983                                                                             10                                                210                    0.8408                                                                             20                                                210                    0.8306                                                                             30                                                210                    0.8028                                                                             40                                                210                   0.7943                                                                             50                                                 210                   0.7576                                                                              60                                                210                   0.7031                                                                              70                                                210                   0.5355                                                                              80                                                210                   0.0000                                                                              90                                                220                   1.3054                                                                              0                                                 220                   0.8784                                                                              10                                                220                   0.8136                                                                              20                                                220                   0.8122                                                                              30                                                220                   0.8090                                                                              40                                                220                   0.7492                                                                              50                                                220                   0.7307                                                                              60                                                220                 0.6978                                                                                 70                                               220                 0.5904                                                                                 80                                               220                 0.0000                                                                                 90                                               230                 1.3054                                                                                 0                                                230                 0.8784                                                                                 10                                               230                 0.8136                                                                                 20                                               230                 0.8122                                                                                 30                                               230                 0.8090                                                                                 40                                               230                 0.7492                                                                                 50                                               230                 0.7307                                                                                 60                                               230                 0.6978                                                                                 70                                               230                 0.5904                                                                                 80                                               230                 0.0000                                                                                 90                                               240                 1.1547                                                                                  0                                               240                 0.8983                                                                                 10                                               240                 0.8408                                                                                 20                                               240                 0.8306                                                                                 30                                               240                 0.8028                                                                                 40                                               240                 0.7943                                                                                 50                                               240                 0.7576                                                                                 60                                               240                 0.7031                                                                                 70                                               240                 0.5355                                                                                 80                                               240                 0.0000                                                                                 90                                               250                 1.0642                                                                                  0                                               250                 0.9320                                                                                 10                                               250                 0.9017                                                                                 20                                               250                 0.8712                                                                                 30                                               250                 0.8620                                                                                 40                                               250                  0.8290                                                                                50                                               250                  0.7970                                                                                60                                               250                 0.7253                                                                                  70                                              250                  0.4896                                                                               80                                                250                  0.0000                                                                               90                                                260                  1.0154                                                                                0                                                260                  0.9663                                                                                10                                               260                  0.9381                                                                                20                                               260                  0.9151                                                                                30                                               260                  0.8871                                                                                40                                               260                  0.8701                                                                                50                                               260                  0.8498                                                                                60                                               260                  0.7762                                                                                70                                               260                  0.4191                                                                                80                                               260                  0.0000                                                                                90                                               270                  1.0000                                                                                 0                                               270                  0.9640                                                                                10                                               270                  0.9345                                                                                20                                               270                  0.8853                                                                                30                                               270                  0.8304                                                                                40                                               270                  0.7945                                                                                50                                               270                  0.7364                                                                                60                                               270                  0.6894                                                                                70                                               270                  0.3913                                                                                80                                               270                  0.0000                                                                                90                                               280                  1.0154                                                                                0                                                280                  0.9663                                                                                10                                               280                  0.9381                                                                                20                                               280                  0.9151                                                                                30                                               280                  0.8871                                                                                40                                               280                  0.8701                                                                                50                                               280                  0.8498                                                                                60                                               280                  0.7762                                                                                70                                               280                  0.4191                                                                                80                                               280                  0.0000                                                                                90                                               290                  1.0642                                                                                0                                                290                  0.9320                                                                                10                                               290                  0.9017                                                                                20                                               290                  0.8712                                                                                30                                               290                  0.8620                                                                                40                                               290                  0.8290                                                                                50                                               290                  0.7970                                                                                60                                               290                  0.7253                                                                                70                                               290                  0.4896                                                                                80                                               290                  0.0000                                                                                90                                               300                   1.1547                                                                              0                                                 300                  0.8983                                                                                10                                               300                  0.8408                                                                                20                                               300                  0.8306                                                                               30                                                300                  0.8028                                                                               40                                                300                  0.7943                                                                               50                                                300                  0.7576                                                                               60                                                300                  0.7031                                                                               70                                                300                  0.5355                                                                               80                                                300                  0.0000                                                                               90                                                310                  1.3054                                                                               0                                                 310                  0.8784                                                                               10                                                310                  0.8136                                                                               20                                                310                  0.8122                                                                               30                                                310                  0.8090                                                                               40                                                310                  0.7492                                                                               50                                                310                  0.7307                                                                               60                                                310                  0.6978                                                                               70                                                310                  0.5904                                                                               80                                                310                   0.0000                                                                              90                                                320                   1.3054                                                                              0                                                 320                   0.8784                                                                              10                                                320                   0.8136                                                                              20                                                320                   0.8122                                                                              30                                                320                   0.8090                                                                              40                                                320                   0.7492                                                                              50                                                320                   0.7307                                                                              60                                                320                   0.6978                                                                              70                                                320                   0.5904                                                                              80                                                320                   0.0000                                                                              90                                                330                   1.1547                                                                               0                                                330                   0.8983                                                                              10                                                330                   0.8408                                                                              20                                                330                   0.8306                                                                              30                                                330                   0.8028                                                                               40                                               330                   0.7943                                                                               50                                               330                   0.7576                                                                              60                                                330                   0.7031                                                                              70                                                330                   0.5355                                                                              80                                                330                   0.0000                                                                              90                                                340                   1.0642                                                                              0                                                 340                   0.9320                                                                              10                                                340                   0.9017                                                                              20                                                340                   0.8712                                                                              30                                                340                   0.8620                                                                              40                                                340                   0.8290                                                                              50                                                340                   0.7970                                                                              60                                                340                   0.7253                                                                              70                                                340                   0.4896                                                                              80                                                340                   0.0000                                                                              90                                                350                   1.0154                                                                              0                                                 350                   0.9663                                                                              10                                                350                   0.9381                                                                              20                                                350                  0.9151                                                                               30                                                350                  0.8871                                                                               40                                                350                  0.8701                                                                               50                                                350                  0.8498                                                                               60                                                350                  0.7762                                                                               70                                                350                  0.4191                                                                               80                                                350                  0.0000                                                                               90                                                ______________________________________                                    

We claim:
 1. An optical position tracking system for determining theposition of an object, comprising:a reflector affixed to the object; alight source; a light detector having a detection surface, a maskpositioned a predetermined distance from said detection surface, and abaffle positioned in a region between said mask and said detectionsurface, said baffle partitioning said region into sections, said lightdetector generating signals representative of light incident on saiddetection surface.
 2. A position tracking system as defined in claim 1,wherein said light detector comprises a plurality of sensors, eachgenerating signals representative of light incident on a distinctsection.
 3. A position tracking system as defined in claim 1, whereinsaid light source has an emitter surface and an emitter mask positioneda predetermined distance from said emitter surface.
 4. A positiontracking system as defined in claim 3, wherein said light source has adiffusely reflective emitter cavity having an emitter aperture thatprovides said emitter surface.
 5. A position tracking system as definedin claim 1, wherein said light source comprises a scanning lightmechanism.
 6. A position tracking system as defined in claim 1, whereinsaid light source comprises a pulse emitter.
 7. A position trackingsystem as defined in claim 1, wherein said light detector has adiffusely reflective detection cavity having a detection aperture thatprovides said detection surface, and said baffle includes an extendedportion that divides said cavity.
 8. A position tracking system asdefined in claim 1, wherein said baffle includes two intersectingmembers that form four of said sections.
 9. A position tracking systemas defined in claim 1, wherein said mask and said baffle have diffuselyreflective surfaces.
 10. A position tracking system as defined in claim1, further comprising a processor that processes said signals from saidlight detector.
 11. A position tracking system as defined in claim 2,further including a second reflector, and said light detector includes asecond plurality of sensors, each of said second sensors also generatingsignals representative of light incident on said respective distinctsection.
 12. A position tracking system as defined in claim 4, whereinsaid detector mask of said light detector has a structure that isconfigured with said emitter cavity of said light source.
 13. A positiontracking system for determining the position of an object, comprising:alight source affixed to said object; a light detector including:adetection surface; a mask positioned a predetermined distance from saiddetection surface; a baffle positioned in a region between said mask andsaid detection surface, said baffle dividing said region into sections.14. A position tracking system as defined in claim 13, wherein saidlight detector includes a diffusely reflective cavity having an aperturethat provides said detection surface.
 15. A position tracking system asdefined in claim 14, wherein said baffle includes an extended portionthat divides said cavity.
 16. An optical position tracking system fordetermining the position of an object, comprising:a reflector affixed tothe object; a diffusely reflective cavity having an aperture; a maskpositioned a predetermined distance from said aperture; a light source;a light detector; a baffle having members that divide a region betweensaid cavity and said mask into sections, wherein said light detectorgenerates signals representative of light incident on said aperture. 17.An optical position tracking system as defined in claim 16, wherein saidlight detector includes a plurality of sensors, each of which isassociated with a distinct section.
 18. An optical position trackingsystem as defined in claim 16, wherein said light source comprises aplurality of emitters, each positioned within a distinct section.
 19. Aposition tracking system as defined in claim 16, wherein said lightsource emits pulses of radiation.
 20. An optical position trackingsystem as defined in claim 16, wherein said baffle has a first portionextending below said aperture and a second portion extending above saidaperture, said first portion dividing said cavity into lower sections,said second portion forming upper sections between said aperture andsaid mask, and said light detector comprises a plurality of sensors,each of which is positioned within a distinct upper section.
 21. Anoptical position tracking system as defined in claim 16, wherein saidbaffle has a first portion extending below said aperture and a secondportion extending above said aperture, said first portion dividing saidcavity into lower sections, said second portion forming upper sectionsbetween said aperture and said mask, and said light source comprises aplurality of emitters, each of which is positioned within a distinctupper section.
 22. A position tracking system as defined in claim 16,wherein said mask and said baffle have diffusely reflective surfaces.23. A position tracking system as defined in claim 16, furthercomprising a processor processing said signals to provide directionaldata of said object.
 24. A position tracking system as defined in claim17, wherein said light source comprises a second diffusely reflectivecavity having an emitter aperture and an emitter mask positioned apredetermined distance from said emitter aperture.
 25. A positiontracking system as defined in claim 18, wherein said light detectorcomprises a second diffusely reflective cavity having a detectionaperture and a detection mask positioned a predetermined distance fromsaid detection aperture.
 26. A position tracking system as defined inclaim 18, wherein each of said emitters is of a distinguishable spectralcharacteristic.
 27. A position tracking system as defined in claim 17,further including a second reflector, wherein said light detectorincludes a second plurality of sensors, each of which is associated witha distinct section.
 28. A position tracking system as defined in claim17, wherein said sensors detect light intensity.
 29. A position trackingsystem as defined in claim 16, wherein said light source emits pulses ofradiation and said light detector measures elapsed time of said pulses.30. A position tracking system as defined in claim 16, wherein saidcavity is hemispherical.
 31. A position tracking system as defined inclaim 16, wherein said light source includes a scanning light mechanism.32. A position tracking system for determining the position of anobject, comprising:a reflector affixed to said object; a scanning lightmechanism generating a radiation beam; a light detector having twoportions each configured to provide a diffusely reflective cavitydefining an aperture and including a mask positioned above saidaperture, said detector generating signals in response to detection oflight; a processor that processes said signals to provide directionaldata representative of a directional location of said reflector.
 33. Aposition tracking system as defined in claim 32, wherein said scanninglight mechanism includes a light source generating a light beam and apositioner that moves the light beam in a predetermined pattern.
 34. Aposition tracking system for determining the position of an object,comprising:a reflector affixed to the object; a scanning light mechanismgenerating a radiation beam; a light detector having two portions eachconfigured to provide a diffusely reflective cavity defining an apertureand including a mask positioned above the aperture, the detectorgenerating signals in response to detection of light, wherein each ofthe portions further includes a baffle that divides each of the cavitiesinto lower sections and a region between the respective mask and therespective aperture into upper sections; and a processor responsive tothe signals for providing directional data representative of adirectional location of the reflector.
 35. A position tracking systemfor determining the position of an object, comprising:a light sourceaffixed to said object; a light detector including a detection surface,a mask positioned a predetermined distance from said detection surface,and a baffle that divides a region between said detection surface andsaid mask into sections; and a plurality of sensors, each associatedwith a distinct section.
 36. A position tracking system as defined byclaim 35, wherein said light detector includes a diffusely reflectivecavity having an aperture that provides said detection surface, and saidbaffle has an extended portion that divides said cavity.
 37. A positiontracking system as defined in claim 36, wherein said cavity ishemispherical and has an interior surface that is diffusely reflective.38. A position tracking system as defined in claim 35, wherein saidbaffle includes two intersecting planar members that form four sections.39. A position tracking system as defined in claim 35, wherein said maskand said baffle have diffusely reflective surfaces.
 40. A positiontracking system as defined in claim 35, further comprising a processor,associated with the detector, for processing said signals to providedirectional signals indicative of a directional location of said object.41. An optical device, comprising:a first structure having a firstoptical surface that faces a first direction; a second structure havinga second optical surface that faces a second direction; said first andsecond structures situated angularly offset from each other wherein eachof said structures masks the optical surface of the other from eitheremitted radiation from or incidental radiation on said other opticalsurface within a distinct range of angles relative to said opticaldevice.
 42. An optical detector in accordance with claim 41, whereinsaid first and second optical surfaces are substantially normal to eachother.
 43. An optical detector in accordance with claim 41, wherein saidrange of angles are substantially at an horizon defined relative to thedevice.
 44. An optical detector comprising:a detection structure of aclosed configuration defining a nonoptical area therein, having at leasttwo distinct substantially equal portions with substantially equaldetection surfaces around said area, each of said portions generating asignal responsive to incidental radiation thereon and including:a firstdetection surface and a second detection surface projecting therefrom atan angle wherein each of said first and second detection surfaces facesa nonparallel direction with respect to the other.
 45. An opticaldetector of claim 44, wherein said direction of said second detectionsurface is parallel with an axis substantially normal to a plane definedby said area and said first detection surface is substantially normal tosaid first detection surface.
 46. An optical detector of claim 44,wherein said detection structure is configured as a closed loop withfour portions.
 47. An optical detector of claim 44, wherein said angleis substantially 90 degrees.
 48. An optical detector of claim 44,wherein said first detection surface faces inwardly toward said openingand said second detection surface faces substantially normally thereto.49. An optical detector of claim 44 wherein said detection surface issensitive to infrared radiation.
 50. An optical detector, comprising:abase configured with a plurality of separate detection surfaces; a maskstructure positioned a predetermined distance from all of said detectionsurfaces; a plurality of detector elements, each of which providessignals representative of light incident on a distinct detectionsurface.
 51. An optical detector as defined in claim 50, wherein saidbase includes a common plurality of diffusely reflective cavities, eachof which provides a distinct detection surface and housing a distinctdetector element.
 52. An optical device, comprising:a base configuredwith a plurality of separate emitter surfaces; a mask structurepositioned a predetermined distance from all of said emitter surfaces; aplurality of emitter elements, each of which provides illumination for adistinct emitter surface.
 53. An optical position tracking systemcomprising:a source of light for association with an object to betracked; a light detector oriented to receive light from a predeterminedarea which includes the object to be tracked, said light detectorcomprising a sensor having an aperture and a mask constructivelyoccluding said aperture in such a manner that a cross-sectional area ofthe aperture presented to incident light is substantially constant overa range of angles of incidence; and processing circuitry for determiningposition of the source of light in response to a detection signal outputof the sensor.
 54. An optical position tracking system as in claim 53,wherein:the source of light comprises a reflector for attachment to anobject to be tracked; and the system further comprises a illuminatorproviding substantially uniform illumination over all azimuths of ahemisphere covering the predetermined area.
 55. An optical positiontracking system as in claim 54, wherein the illuminator comprises anillumination source and a mask constructively occluding a portion of theillumination source.
 56. An optical position tracking systemcomprising:a reflector for attachment to an object to be tracked; alight distributor, comprising an illumination source and a maskconstructively occluding a portion of the illumination source, foruniformly illuminating all azimuths and elevations of a hemisphericalregion; a light detector oriented to receive light reflections fromwithin the region and provide a signal representative of a direction andintensity of incident light; and processing circuitry for determiningposition of the reflector in response to a detection signal output ofthe sensor.
 57. An optical position tracking system as in claim 56,wherein the light detector comprises:a sensor having an aperture; and amask constructively occluding said aperture in such a manner that across-sectional area of the aperture presented to incident lightreflections is substantially constant over a range of angles ofincidence in a hemispherical region facing the light detector.
 58. Anoptical position tracking system comprising:a reflector for attachmentto an object to be tracked; a light distributor, comprising anillumination source and a mask constructively occluding a portion of theillumination source, for uniformly illuminating a predetermined area; alight detector oriented to receive light reflections from thepredetermined area, said light detector comprising a sensor having anaperture and a mask constructively occluding said aperture in such amanner that a cross-sectional area of the aperture presented to incidentlight reflections is substantially constant over a range of angles ofincidence; and processing circuitry for determining position of thereflector in response to a detection signal output of the sensor.
 59. Anoptical position tracking system comprising:a constructed occlusionirradiation device oriented to uniformly irradiate a predeterminedregion; a constructed occlusion radiation detector oriented to uniformlysense radiation reflected from within the predetermined region; and aprocessing system responsive to at least one output signal from thedetector for determining a position of a reflective object within thepredetermined region.
 60. An optical position tracking systemcomprising:a source of light for association with an object to betracked; a light detector oriented to receive light from a predeterminedarea which includes the object to be tracked, said light detectorcomprising a sensor having an aperture and a mask shielding a portion ofsaid aperture from incident light in such a manner that across-sectional area of the aperture presented to incident light issubstantially constant over a range of angles of incidence; andprocessing circuitry for determining position of the source of light inresponse to a detection signal output of the sensor.
 61. An opticalposition tracking system comprising:a source of light for associationwith an object to be tracked; a light detector oriented to receive lightfrom a predetermined area which includes the object to be tracked, thelight detector comprising:a sensor having an aperture, a mask shieldinga portion of the aperture from incident light in such a manner that across-sectional area of the aperture presented to incident light issubstantially constant over a range of angles of incidence, and a lightdeflector positioned between the aperture and the mask; and processingcircuitry for determining position of the source of light in response toa detection signal output of the sensor.
 62. An optical positiontracking system as in claim 60, wherein the light detector furthercomprises a diffusely reflective cavity oriented to redirect lighttoward the sensor, and an opening of the cavity defines the aperture.63. An optical position tracking system comprising:a source of light forassociation with an object to be tracked; a light detector oriented toreceive light from a predetermined area which includes the object to betracked, the light detector comprising:a sensor having an aperture, amask shielding a portion of the aperture from incident light in such amanner that a cross-sectional area of the aperture presented to incidentlight is substantially constant over a range of angles of incidence, anda reflective baffle dividing a region between the aperture and the maskinto a plurality of sub-regions; processing circuitry for determiningPosition of the source of light in response to a detection signal outputof the sensor, wherein the sensor comprises a plurality of sensors eachof which is oriented to sense light passing through a distinct one ofthe sub-regions.
 64. An optical position tracking system as in claim 63,wherein the baffle divides the region into sections.
 65. An opticalposition tracking system as in claim 60, wherein:the source of lightcomprises a reflector for attachment to an object to be tracked; and thesystem further comprises an illuminator providing substantially uniformillumination over all azimuths of a hemisphere covering thepredetermined area.
 66. An optical position tracking system as in claim60, wherein the source of light comprises a pulse emitter.
 67. Anoptical position tracking system as in claim 60, wherein the source oflight comprises a scanning light emitter.
 68. An optical positiontracking system as in claim 60, wherein the light detectordifferentiates light of different colors.
 69. An optical positiontracking system comprising:a reflector for attachment to an object to betracked; a light distributor, comprising an illumination source and amask intercepting light from a portion of the illumination source, suchthat the light distributor uniformly illuminates all azimuths andelevations of a hemispherical region; a light detector oriented toreceive light reflections from within the region and provide at leastone signal representative of direction and intensity of incident light;and processing circuitry for determining position of the reflector inresponse to a detection signal output of the detector.
 70. An opticalposition tracking system as in claim 69, wherein the light detectorcomprises:a sensor having an aperture; and a mask shielding a portion ofsaid aperture in such a manner that a cross-sectional area of theaperture presented to incident light reflections is substantiallyconstant over a range of angles of incidence in a hemispherical regionfacing the light detector.
 71. An optical position tracking system as inclaim 69, wherein the distributor further comprises a light deflectorpositioned between the illumination source and the mask.
 72. An opticalposition tracking system as in claim 69, wherein:the light distributorfurther comprises a reflective baffle dividing a region between theillumination source and the mask into a plurality of sub-regions, andthe illumination source comprises a plurality of emitters each of whichis oriented to radiate through a distinct one of the sub-regions.
 73. Anoptical position tracking system as in claim 72, wherein the baffledivides the region into sections.
 74. An optical position trackingsystem comprising:a reflector for attachment to an object to be tracked;a light distributor, comprising an illumination source and a maskintercepting light from a portion of the illumination source, such thatthe light distributor uniformly illuminates a predetermined area; alight detector oriented to receive light reflections from thepredetermined area, said light detector comprising a sensor having anaperture and a mask shielding a portion of said aperture from incidentlight in such a manner that a cross-sectional area of the aperturepresented to incident light reflections is substantially constant over arange of angles of incidence; and processing circuitry for determiningposition of the reflector in response to a detection signal output ofthe sensor.
 75. An optical position tracking system as in claim 74,wherein the light detector further comprises a light deflectorpositioned between the aperture and the detector mask.
 76. An opticalposition tracking system as in claim 75, wherein:the light deflectorcomprises a reflective baffle dividing a region between the aperture andthe detector mask into a plurality of sub-regions, and the sensorcomprises a plurality of sensors each of which is oriented to senselight passing through a distinct one of the sub-regions.
 77. An opticalposition tracking system as in claim 76, wherein the baffle divides theregion into sections.
 78. An optical position tracking system as inclaim 75, wherein the light detector further comprises a diffuselyreflective cavity redirecting incident light toward the sensor, anopening of the cavity defining the aperture.
 79. An optical positiontracking system as in claim 74, wherein the distributor furthercomprises a light deflector positioned between the illumination sourceand the distributor mask.
 80. An optical position tracking system as inclaim 79, wherein:the light deflector comprises a reflective baffledividing a region between the illumination source and the distributormask into a plurality of sub-regions, and the illumination sourcecomprises a plurality of emitters each of which is oriented to radiatethrough a distinct one of the sub-regions.
 81. An optical positiontracking system as in claim 80, wherein the baffle divides the regioninto sections.
 82. An optical position tracking system as in claim 79,wherein the illumination source comprises a diffusely reflective cavityand an emitter for radiating light into the cavity, the distributor maskintercepting light emerging from an opening of the cavity.
 83. Anoptical position tracking system as in claim 81, wherein the emitterradiates pulses of light into the cavity.
 84. A position tracking systemfor determining azimuthal position of an object relative to the system,comprising:a light source associated with said object; a light detectorincluding:a detection surface; a mask positioned a predetermineddistance from said detection surface; a baffle positioned in a regionbetween said mask and said detection surface, said baffle dividing saidregion into sections.
 85. An optical position tracking system as inclaim 84, wherein the surface has a surface width and the mask has amask width, said mask width being greater than said surface width. 86.An optical position tracking system as in claim 84, wherein the surfacehas a surface width and the mask has a mask width, said mask width beinglesser than said surface width.
 87. An optical position tracking systemas in claim 84, wherein the surface has a surface width and the mask hasa mask width, said mask width being substantially equal to said surfacewidth.
 88. An optical position tracking system as in claim 84, furthercomprising a cavity having an aperture that provides said surface, saidbaffle dividing said cavity into active and nonactive sections.
 89. Anoptical position tracking system as in claim 88, wherein each of saidactive sections houses an optical element.